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LIBRARY OF CONGRESS. 



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Chap.. Copyright No*.. 

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UNITED STATES OF AMERICA. 



A SYLLABUS 



OF 



LECTURES 



ON 



THE BRAIN AND SPINAL CORD 



DELIVERED BEFORE 



THE SOPHOMORE AND JUNIOR CLASSES 

BY 

HARRIS E. SANTEE, A. B, M. D., 

Professor of Anatomy, 

Harvey Medical College, 

Chicago. 



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L431 

Copyrighted by H. E. Santee, 
November, 1898. 




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MENINGES OF BRAIN AND SPINAL CORD. 



Three membranes invest the brain and spinal cord. From 
without inward, they are the Dura materfArachnoid and Pia 
mater. 

DURA MATER OF THE BRAIN. 

Structure— It is a strong", fibro-elastic membrane lined with 
endothelium. Its functions are endosteum of the skull and outer 
protective covering of the brain. 

Relations — At foramina it is continuous with periosteum, and 
it is adherent along the sutures of the skull, elsewhere it is loosely 
attached. 

Processes — From the inner surface of the dura the great pro- 
cesses are given off. The falx cerebri and falx cerebelli hang 
vertically in the great longitudinal fissure of the cerebrum and 
the posterior notch of the cerebellum; and, into the great trans- 
verse fissure, extends horizontally the tentorium cerebelli. The 
falx cerebri is attached in front to the crista galli and behind to 
the internal occipital protuberance and superior surface of the 
tentorium; the falx cerebelli continues from the inferior surface of 
the tentorium along the occipital crest to the posterior border of 
the foramen magnum. The attachment of the tentorium cerebelli 
is to the internal occipital protuberance, and the lateral arms of 
the crucial ridge forward to the petrous bone; and, then, along 
the superior border of the petrous bone to the clinoid processes 
of the sphenoid. A large mesial foramen between its anterior 
border and the dorsum ephipii transmits the mid-brain. 

Sinuses. — Large venous passages lined with endothelial cells, 
and called sinuses, are situated between the layers of the dura. 
In the convex and in the free border of the falx cerebri are, re- 
spectively, the superior and the inferior longitudinal sinuses. 
The superior extends from the foramen caecum back to the tor- 
cular Herophili at the internal occipital protuberance. Joining 
the veins of Galen, at the margin of the tentorium, the inferior 



4 The Brain and Spinal Cord. 

longitudinal sinus becomes the straight, whose course is through 
the middle of the tentorium to the torcular. The occipital sinus 
(or sinuses) traverses the falx cerebelli from the foramen magnum 
upward to the same point. In the torcular Herophili the lateral 
sinuses arise. Grooving the horizontal arms of the crucial ridge, 
each runs outward in the tentorium to the base of the petrous bone, 
where it receives the superior petrosal sinus; it then turns down- 
ward through the signoid fossa and unites with the inferior pe= 
trosal sinus in the jugular foramen. Situated on either side of 
the sella Turcica is a continuation of the ophthalmic vein, the 
large cavernous sinus whose division at the apex of the petrous 
bone forms the two petrosal sinuses. The circular sinus (around 
the sella) joins the two cavernous to each other; and the inferior 
petrosal communicate with one another through the transverse 
or basilar sinus. The petrosal sinuses, from the bifurcation of 
the cavernous, follow outward the corresponding border of the 
petrous bone; the superior empties into the lateral, and the infe- 
rior unites with the lateral in forming the internal jugular vein. 

Along and within the superior longitudinal sinus are the Pac- 
chionian bodies. They are enlarged villi of the arachnoid, and 
seem to afford an outlet for the sub-arachnoid fluid into the supe- 
rior longitudinal sinus. 

The arteries which supply the dura are the anterior and pos- 
terior ethmoidal; the anterior meningeal; the great and small 
meningeal; branches of the ascending pharyngeal and occipital; 
and the posterior meningeal. 

The following nerves give branches to the dura: — pathetic, 
ophthalmic, Gasserian ganglion and twelfth cranial; and the 
sympathetic. 

Four points of difference in dura of the cord — absence of 
processes, of sinuses, of Pacchionian bodies, and of periosteal 
function. The meningo-rachidian veins separate it from the ver- 
tebrae. It forms part of the central ligament of the spinal cord. 

arachnoid of brain. 

In structure it is a delicate, fibrous, web-like membrane cov- 
ered externally with endothelium. Internally, it is joined to pia 
mater by innumerable fibrous trabecule, the subarachnoid tissue. 

The trabecular and all spaces formed by them possess a single 
layer of endothelial cells. Conical elevations of fibrous tissue with 



Meninges of Brain and Spinal Cord. 5 

their investing endothelium constitute the villi seen on the outer 
surface. 

Relations— The arachnoid follows the inner surface of the 
dura. It does not dip into the sulci. From the pia it is separated 
by the subarachnoid spaces. The anterior subarachnoid 
space, in front of the pons and between the temporal lobes of the 
cerebrum; and the posterior between the medulla and cerebel- 
lum, contain most of the subarachnoid fluid. The posterior 
communicates with fourth ventricle through the foramen of Ma- 
jendie (and foramina of Key and Retzius.) 

The vessels seen for a short distance in the arachnoid belong 
to the pia mater. Its nerves are doubtful. Perhaps branches of 
the inferior maxillary, of the facial and of the spinal accessory 
supply it. 

In the arachnoid of the cord fewer trabeculae join it to the 
pia; and these, in great part, are collected to form a fenestrated 
septum in the posterior median line. The medulli spinal veins 
are covered by the arachnoid, lying between it and the pia. 

PIA MATER OF THE BRAIN. 

Structure— It is a vascular me??ibrane composed of a close 
net-work of veins and arteries held together by fibro-elastic areo- 
lar tissue. The endothelium covering its outer surface is contin- 
uous with that of the subarachnoid trabeculae and spaces. Rela- 
tions — The pia closely follows the brain surface. Internally, it 
sends supporting trabeculae into the brain, which transmit blood 
vessels. Two important processes are formed by it: the velum 
interpositum (helping to form the anterior choroid tela) is tucked 
into the great transverse fissure between the fornix and the inter- 
brain. A second process is tucked in over the fourth ventricle, be- 
tween the medulla and cerebellum. It helps to form the posterior 
choroid tela, which roofs over the posterior part of the fourth ven- 
ticle. The posterior choroid tela is pieroed by three foramina 
(Majendie, and Key and Retzius). They open into the fourth ven- 
tricle. 

The arteries of the pia are the anterior, middle and posterior 
cerebral; and the anterior and posterior inferior cerebellar and 
superior cerebellar with many branches. 

Veins are numerous in the pia; the veins of Galen and of the 
choroid plexuses of the lateral, third and fourth ventricles; cere- 



6 The Brain and Spinal Cord. 

bral veins, superior, mesial and inferior; and superior, lateral and 
inferior cerebellar veins. All of them empty into the sinuses. 

Seven cranial nerves— 3d, 5th, 6th, and 7th, gth, 10th and nth — 
and the sympathetic supply the pia mater. 

The pia of the cord is much stronger than that of the brain. 
It has two distinct layers, of which the inner is continuous with 
the brain pia. Both layers dip into the anterior median fissure; 
only the inner dips into the posterior fissure. The outer layer 
forms the linea splendens in front, and the ligamentum denti- 
culatum on either side. The teeth of the dentate ligament in- 
vested with arachnoid, are attached to the dura opposite the upper 
twenty vertebra. The filum terminale is the pial extension below 
the cord and with similar extensions of the arachnoid and dura 
forms its central ligament. For some distance the filum contains 
gray matter continuous with the spinal cord. The pia of the cord 
is supplied by sympathetic nerves, and contains the ramifications 
of one anterior and two posterior spinal arteries and of the me- 
dulli-spinal veins. 



GRAND DIVISIONS OF BRAIN. 



The brain maybe conveniently studied in four grand divisions : 

I. Cerebrum, composed of — 

1 . He?nispheres y which include: 

Their cortex and medulla, 
Corpora striata, and 
Olfactory lobes, 

With connecting links of the hemispheres: 

Corpus callosum, 

Fornix and 

Anterior commissure (and) 

2. Inter-Brain, which includes: 

Lamina cinerea, 

Tuber cinereum and infundibulum, 

Corpora albicantia, 

Optic thalami, 

Middle commissure, and posterior (in part). 
Pineal body. 

External geniculate bodies. 
Optic tracts and commissure. 

II. Mid- Brain, composed of — 

Crustae, or peduncles of cerebrum. 

Substantia nigra. 

Tegmentum. 

Corpora quadrigemina. 

Internal geniculate bodies. 

III. Hind- Brain — 

Pons. 
Cerebellum. 

IV. After- Brain — 

Medulla. 



THE CEREBRUM. 



FISSURES OF THE CONVEX SURFACE. 

Two fissures are very extensive. The great longitudinal fis= 

sure separates the hemispheres of the cerebrum. It contains the 
falx cerebri. The cerebrum is separated from the cerebellum by 
th£ great traverse fissure; This fissure continues forward above 
the mid-brain, and terminates between the inter-brain and the 
hemisphftes in the cerebrum. The tentorium occupies its poste- 
rior part. Anteriorly it contains the velum interpositum. Three 
interlobular fissures are found in each hemisphere: 

(i) The fissure of Sylvius begins in the vallecula at the base 
of the brain. It runs outward between the frontal and the tempo- 
ral lobe, along the lesser wing of the sphencid bone; and, turning 
upward, on the convex surface it divides into an anterior, a ver- 
tical and a horizontal ramus. Into the frontal lobe project the 
small anterior and vertical rami. The horizontal limb separates 
the temporal lobe from the parietal. Near the crotch and within 
the fissure of Sylvius is situated the island of Reil. A line drawn 
from a point, \% inches behind the external angular process of 
the frontal bone and \% inches above the zygoma, backward to a 
point, % of an inch below the parietal eminence, lies directly over 
the horizontal ramus of this fissure. 

(2) Beginning just above the horizontal limb of the fissure of 
Sylvius, is the fissure of Rolando, or Central fissure, which 
extends upward and backward almost to the great longitudinal 
fissure. Its upper extremity is about half an inch behind the 
middle of a line drawn from the nasal eminence to the external 
occipital protuberance (the sagittal meridian). With this line the 
fissure of Rolando forms an anterior angle of 67 degrees. The 
fissure of Rolando forms the boundary between the frontal and 
the parietal lobe. 

(3) If the line locating the horizontal limb of the fissure of 
Sylvius be extended back to the sagittal meridian its posterior 



The Cerebrum. 9 

end marks the location of the parietooccipital fissure, (external 
part). The greater part of this fissure is on the internal or mesial 
surface of the hemisphere. To the extent of half an inch the 
external parieto-occipital fissure separates the parietal and occip- 
ital lobes from each other. 

LOBES OF CONVEX SURFACE. 

(1) The frontal lobe comprises the anterior polar region of 
the hemisphere back to the Rolandic and the Sylvian fissure. 
It is subdivided by three sulci: the precentral sulcus, which is 
parallel with the fissure of Rolando (central), and the superior and 
ijiferior frontal sulci. The two latter extend downward and for- 
ward from the precentral sulcus and separate from each other the 
superior, middle and inferior frontal convolutions. The 
ascending frontal convolution lies between the precentral 
sulcus and the fissure of Rolando It is joined to the ascending 
parietal convolution by the paracentral lobule, above the cen- 
tral fissure; and by the operculum, below it. The operculum 
and posterior part of the inferior frontal gyrus constitute the 
region of speech. 

(2) The parietal lobe is situated behind the fissure of Rolando 
and above the horizontal limb of the Sylvian fissure. From the 
posterior end of the latter to the external parieto-occipital fissure, 
the lobe is separated from the temporal, below, and the occipital, 
behind, by an imaginary line. The sulci of this lobe are the in- 
traparietal with an anterior and a posterior ramus (joined by the 
genu) which are parallel with the central and the great longitudi- 
nal fissures, respectively; and the post-central sulcus which 
ascends from near the genu of the intraparietal. The anterior 
limb of the latter and the post-central sulcus separate the ascend- 
ing parietal convolution from the superior parietal and inferior 
parietal. Indefinite sulci subdivide the inferior parietal into supra- 
marginal and angular gyri. The second annectant convolution 
joins the angular gyrus to the middle occipital. The supramargi- 
nal and angular convolutions contain part of the visual center. 
The best known motor areas of the cortex are contained in the 
ascending frontal, ascending parietal and superior parietal con- 
volutions. 

(3) Occipital lobe— It forms the posterior pole of the hemi- 
sphere. With the parietal and temporal lobes it is directly con- 



io The Brain and Spinal Cord. 

tinuous. The parieto-occipital fissure bounds it to the extent of 
half an inch. The superior occipital sulcus, vertical in direction, 
and the iniddle and inferior, which are horizontal, divide the lobe 
into superior, middle and inferior convolutions. A part of the 
center of vision is located in the middle occipital gyrus. 

(4) The temporal lobe is that part of the cerebral hemisphere 
behind the main stem and below the horizontal limb of the fissure 
of Sylvius. It rests in the middle fossa of the skull; and is 
probably the seat of the centers of taste, of smell and of hear- 
ing. The first temporal sulcus (or parallel sulcus) and the second 
temporat sulcus divide the lobe into three horizontal convolutions, 
named, from the Sylvian fissure downward, the first, second and 
third temporal convolutions. 

Annectant convolutions are small links joining the greater 
gyri. The first annectant joins the superior parietal and superior 
occipital convolutions. To the middle occipital gyrus the angu- 
lar is linked by the second annectant and the middle temporal 
by the third. The fourth annectant unites the inferior temporal 
and inferior occipital convolutions. There are other less con- 
stant annectants. 

(5) The island of Reil is also called the central lobe. Situated 
within the fissure of Sylvius, it is bounded at the base of the brain 
by the sulcus limitans insulce (anterior, external and posterior). 
The sulcus centralis insulce divides it into anterior and posterior 
lobule, each of which is composed of from two to four convolu- 
tions. The operculum and inferior frontal convolution cover 
them, hence the name, gyri operti, also applied to them. 

FISSURES OF MESIAL SURFACE. 

The middle third of this surface is made by sagittal section 
through the connecting links of the hemispheres and the inter- 
brain. The surface presents five fissures: 

(1) Beginning under this middle cut surface and extending 
forward, upward and backward until it half encircles the corpus 
callosum; and then turning upward to the convex border and end- 
ing just behind the fissure of Rolando, is the calloso=marginal 
fissure. It separates the gyrus fornicatus and the marginal con- 
volution from one another by its anterior part; and, by its up- 
turned posterior end, separates the paracentral lobule from the 
quadrate lobe. 



The Cerebrum. ii 

(2) The parietooccipital fissure (internal part) extends up- 
ward and backward from just beneath the thick posterior margin, 
the splenium of the corpus callosum to border of the mesial sur- 
face, where it is continuous with the external parieto-occipital fis- 
sure. It is situated between the quadrate and cuneate lobe. 

(3) From near the middle of the parieto-occipital the calca= 
rine fissure extends in a curve downward and backward be- 
tween the cuneate lobe and the fifth temporal (lingual) convolu- 
tion. 

(4) A crescentic fissure, convex downward, winds from the 
splenium of the corpus callosum forward beneath the optic thala- 
mus nearly to the end of the temporal lobe, where it is closed by 
the uncus. It is the dentate or hippocampal fissure. 

(5) The long collateral fissure is situated below the dentate, 
parieto-occipital and calcarine fissures. The collateral fissure 
bounds, inferiorly, the hippocampal and fifth temporal convolu- 
tion; and separates them from the fourth temporal (or fusiform) 
gyrus. 

LOBES AND CONVOLUTIONS ON MESIAL SURFACE. 

They form two concentric rings, interrupted antero-inferiorly 
at the vallecula Sylvii, which encircle the corpus callosum and 
optic thalamus. The two rings are separate"* from one another 
by a broken fissure, the limbic fissure, made up of the calloso- 
marg'nal (except its posterior end), the post-limbic sulcus, and 
the anterior part of the parieto-occipital and collateral fissures. 

Central ring— The gyrus fornicatus and hippocampal convo- 
lution, joined by the isth?nus at the posterior border of the corpus 
callosum, form the central ring. The former begins under the 
corpus callosum in the frontal lobe anterior to the fissure of Syl- 
vius; and the latter terminates as uncus just behind that fissure 
in the temporal lobe. 

The peripheral ring, from before backward, is composed of 
the marginal convolution, ending in the paracentral lobule; the 
quadrate lobe, bounded antero-inferiorly by the post-limbic sul- 
cus; the cuneate lobe; the fifth temporal convolution (infracal- 
carine or lingual); and the fourth temporal or fusiform convolu- 
tion. A slight sulcus (third temporal), separates the last from the 
third temporal gyrus on the convex surface. 

The uncinate convolution is the combined hippocampal and 
fifth temporal gyri. 



12 The Brain and Spinal Cord. 

Limbic Lobe— It is composed of the following parts, viz.: (i) 
the gyrus fornicatus and hippocampal convolution; (2) the nerves 
of Lancisi and peduncle of corpus callosum; and (3) the pillars 
and half the body of the fornix, one-half of the septum lucidum, 
and the fascia dentata. It is encircled by the limbic fissure. 

BASE OR INFERIOR SURFACE. 

The basal surface of the cerebrum extends from the anterior 
poles of the hemispheres back to the fissure of Sylvius, laterally; 
and, in the median line, to the posterior perforated lamina and 
crustae of the mid-brain. The great longitudinal fissure splits it 
into lateral halves in front, separating the frontal lobes of the 
cerebrum from each other. The fissure extends back to the up- 
turned part (lamina terminalis) of the lamina cinerea and to the 
corpus callosum. The length of the fissure is considerably less 
than one-third of the cerebral axis. 

The mesial structures of this surface named from before 
backward are as follows: 

Lamina cinerea, 

Optic chiasma, 

Tuber cinereum and infundibulum, 

Pituitary body, 

Corpora albicantia. 

These are often called the interpeduncular structures. They 
form a continuous sheet beneath the third ventricle and optic 
thalami, which joins, antero-laterally, the anterior perforated 
lamina and the cortex of the internal orbital convolution. 

The lamina cinerea is the most anterior of the mesial struc- 
tures. It is a thin lamina of ash-colored (cinereum) gray matter. 
Arching over the superior surface of the optic commissure to 
which it is attached, it then turns upward, lamina terminalis, 
and meets the rostrum of the corpus callosum. In the angle of 
turning is the optic recess. The lamina terminalis, which is seen in 
the floor of the great longitudinal fissure, forms part of the ante- 
rior boundary of the third ventricle. 

At the posterior border of the optic commissure, the lamina is 
continuous with the tuber cinereum. Here the gray matter is 
thickened and centrally prominent. The bulbous infundibulum 
projects downward from it to rest in the sella Turcica, where it 
forms the posterior lobe of the pituitary body. The upper part of 



The Cerebrum. 13 

the infundibulum is hollow (funnel-like). Its cavity forms the 
lowest part of the third ventricle. In man the bulb of the infun- 
dibulum is solid in the adult, though hollow in the embryo. It is 
composed of nervous matter and is developed from the floor of 
the Thalamencephalon. From the base (superior end) of the in- 
fundibulum the tuber cinereum extends in continuity with the an- 
terior perforated lamina and sub-thalmic gray matter on each 
side of it; and, behind, the corpora albicantia mark the boundary 
between it and the posterior perforated lamina of the mid-brain. 

The pituitary body is composed of two lobes bound together 
by connective tissue. A sheet of dura mater (diaphragm sellae), 
holds them in the pituitary fossa. The anterior lobe, the larger, 
is derived from the epithelium of the mouth cavity; and, in struc- 
ture, resembles the thyroid gland. Its closed vesicles, lined with 
columnar epithelium (in part ciliated) contain a viscid, jelly-like 
material (pituita) which suggested the name for the body. The 
anterior lobe is hollowed out on its posterior surface and receives 
the posterior lobe, the infundibulum, into the concavity. 

Two white bodies, as large as a small pea, the corpora albi= 
cantia, are situated one on either side of the median line between 
the tuber cinereum and the pigmented gray matter of the poste- 
rior perforated lamina. Each is formed by a loop in the anterior 
pillar of the fornix and is, therefore, composed of white fibers on 
the surface. There is gray matter in the interior, which may 
contain the ends of the fornix fibers and be the seat of origin of 
the ascending bundle, the bundle of Yicq d'Azyr. The latter 
terminates in the optic thalamus. Immediately behind the cor- 
pora albicantia is the posterior perforated lamina. This is the 
exposed part of the substantia nigra of the mid-brain, perforated 
for the passage of the postero-median ganglionic arteries to the 
optic thalami and walls of the third ventricle. The pons and 
crustse bound it behind. Issuing from the inner side of the crusta 
is the large motor oculi, or third cranial, nerve; and coursing over 
its surface from behind forward is the smaller fourth nerve. The 
crustae or cerebral peduncles will be described with the mid-brain 
to which they belong. 

The Optic Chiasma remains to be described. It is situated 
mesially beneath the lamina cinerea, in the optic groove of the 
sphenoid bone. The fibers of the optic nerves and tracts compose 
it. There are four sets of these fibers, viz.: the inter-retinal, inter- 



14 The Brain and Spinal Cord. 

cerebral, direct and decussating. The first are commissural be- 
tween the retinas and do not enter the optic tracts. The interce- 
rebral are not found in the optic nerves, but form a commissure 
(Gudden's) for the internal geniculate bodies. The direct and 
decussating- fibers run through tract and nerve and join the brain 
with the retina of the same and of the opposite side, respectively. 
The optic nerves extend from the front of the commissure into 
the orbits through the optic foramina, and terminate in the rods 
and cones of the retinas. The optic tracts connect the commis- 
sure with the brain. Each tract winds outward and backward 
around the cerebral peduncle, and divides into an internal and an 
external root. The roots wind around the optic thalamus and 
disappear (superficial origin) at the corresponding geniculate 
body. The fibers of the external root may be traced to the optic 
thalamus and occipital lobe, to the external geniculate and the 
anterior quadrigeminal body. Probably some fibers come from 
the cerebellum through the fillet. The internal root arises from 
the optic thalamus and internal geniculate body. 

We come now to the lateral part of the base of the cere- 
brum. 

Orbital Lobe— The inferior surface of the frontal lobe, resting 
on the orbital plate of the frontal bone, is called the orbital lobe. 
It is separated from its fellow by the great longitudinal fissure, 
and is bounded behind by the vallecula Sylvii and fissure of Syl- 
vius, over-lapped by the temporal lobe. More accurately the pos- 
terior boundary is the anterior perforated space and anterior fis- 
sure of Reil. The orbital lobe is divided by an reshaped fis= 
sure, directed fore and aft, into internal, anterior and poste= 
rior orbital convolutions. The internal orbital convolution lies 
beside the great longitudinal fissure, and is continuous with the 
marginal convolution on the mesial surface. Its anterior end joins 
the superior frontal convolution; its posterior, the trigone and area 
of Broca. The internal orbital convolution is subdivided by the 
sulcus olfactorius, which contains the olfactory tract. The anterior 
and posterior orbital convolutions may be traced to the convex 
cerebral surface in continuity with the middle and inferior frontal 
gyri. 

If the anterior part of the temporal lobe be removed, the under 
surface of the island of Reil is brought into view. The sulcus 
limitans insula bounds it on three sides (anterior, external and 



The Cerebrum. 15 

posterior) and separates it from the posterior orbital gyrus in 
front, the inferior frontal and operculum externally, and from the 
temporal lobe behind. (See lobes of convex surface.) 

Olfactory Lobe — This term includes the remainder of the 
structures forming the inferior surface of the cerebrum. The rea- 
son for calling them the olfactory "lobe" is found in the lower 
animals; and in the human embryo, where it exists as a prominent 
hollow process of the cerebral hemisphere. A constriction (fis- 
sura prima) divides this diverticulum into the anterior and the 
posterior olfactory lobule. In the human adult the anterior olfac= 
tory lobule is represented by the bulb, the tract, the trigone and 
the area of Broca. The anterior perforated lamina (or space) 
represents the posterior lobule. 

The olfactory bulb is an ovoid mass of brain matter about a 
half-inch long and one-eighth of an inch in diameter. It rests 
between the orbital lobe and the cribriform plate of the ethmoid 
bone. Below, and on each side, it is composed of cortical gray 
matter (four layers), from which arise the twenty or thirty olfac= 
tory nerves. The nerves, after entering the nasal fossa through 
the cribriform plate, are distributed to the Schneiderian mem- 
brane. In the third layer of the gray matter are found large 
mitral cells whose medullated axis-cylinders, or axons, form the 
white matter of the bulb, and, continued backward, constitute the 

Olfactory tract — The tract is triangular in section, nearly all 
inch long and one line in width. It is concealed in the olfactory 
sulcus. At its base it divides into external and internal root, 
which inclose between them the trigone or middle (gray) root into 
which some fibers may. be traced. The external root courses 
backward and outward and terminates in the uncus at the anterior 
extremity of the hippocampal convolution. It crosses the anterior 
perforated space. The internal root runs backward and mesially 
between the trigone and area of Broca. Its fibers bend upward 
into Broca's area and the gyrus fornicatus. Thus the two roots 
unite the opposite ends of the limbic lobe. From the bifurcation 
of the olfactory tract, a few fibers proceed into the trigone and 
frontal lobe. 

The trigone, the triangular portion of cortex between the inner 
and outer olfactory roots, is continuous with Broca's area. 
The internal root marks the boundary between them. Both are 
bounded behind by the fissura prima (transverse part), and the 



16 The Brain and Spinal Cord. 

oblique part of the same fissure separates the area of Broca from 
the peduncle of the corpus callosum. On the mesial surface, 
Broca's area joins the gyrus fornicatus. Some of the fibers of 
the middle root of the olfactory tract probably pass through the 
anterior commissure; and, after piercing the opposite corpus 
striatum, terminate in the temporal lobe. They constitute the 
only olfactory decussation known. 

The posterior olfactory lobule is identical with the anterior 
perforated lamina. It is separated from the trigone by the trans- 
verse fissura prima. Internally it is in direct continuity with the 
lamina cinerea. The optic tract bounds it behind. Externally it 
forms the floor of the vallecula Sylvii, where it is overlapped by 
the temporal lobe. It corresponds to the inferior surface of the 
corpus striatum. Coursing over the inner and the outer border of 
the anterior perforated lamina, are the collosal peduncle and ex- 
ternal olfactory root, which converge and meet in the hippocampal 
convolution. The perforations of the lamina are for the antero- 
lateral ganglionic arteries. 

general cavity of the cerebrum and its subdivisions. 

Considering all the cerebral cavities together, we notice that 
they form a wedge-like space. In shape the wedge is rectangular 
and stands base upward against the corpus callosum. Its bev- 
eled surfaces look toward the hemispheres. The blade is driven 
downward as if to split the cerebrum into lateral halves, the edge 
resting on the mesial structures at the base of the brain. The 
space is inclosed laterally between the diverging internal cap- 
sules which, within the hemispheres, decussate with the lateral 
extremities of the corpus callosum. The two structures most 
necessary to an understanding of the cerebral cavity, therefore, 
are the internal capsule and corpus callosum. 

Internal capsule — Looking at the base of the brain, we see two 
broad bands of nerve fibers, the crustce or peduncles, issue from the 
front of the pons and, diverging upward and forward, enter the 
hemispheres beneath the optic tracts. The peduncular fibers are 
reinforced by additional fibers within the hemisphere. The fibers 
then radiate toward the cerebral cortex in the form of a hollow 
cone or funnel. This funnel=like group of fibers is the internal 
capsule. The bell of the funnel opens upward and outward and 
contains the lenticular nucleus; its spout (solid), directed toward 



The Cerebrum. 17 

the pons and mesially, is represented by the crusta. Antero-in- 
feriorly the fibers diverge to opposite sides of the fissure ot Sylvius 
and produce a break in the continuity of the funnel. As the in- 
ternal capsule proceeds into the hemisphere, it passes along the 
outer surface of the optic thalamus, but it impales the great 
ganglion of the hemisphere, the corpus striatum, in such manner 
as to place the caudate nucleus and amygdala upon its circum- 
ference and to inclose within its walls (to capsulate) the lenticu- 
lar nucleus. (The lenticular nucleus is separated externally from 
the claustrum by a thin layer of fibers called the external cap- 
sule). 

Laminae — The internal capsule is flattened from above down- 
ward. It has, therefore, a superior and an inferior lamina which, 
posteriorly, are continuous with each other. The inferior lamina 
(or inferior ramus, as seen in section), contains but few fibers and 
is a very thin layer. In front, it ends as a free border. Its fibers 
pass outward beneath the lenticular nucleus and, after winding 
over the amygdala and the descending horn of the lateral ven- 
tricle, terminate in the temporal lobe, — perhaps in the centers of 
taste, smell and hearing. In the angle between the descending 
horn and the body of the lateral ventricle, the inferior lamina 
joins the superior. 

The superior lamina (or superior ramus) of the internal cap- 
sule contains most of the crusta. It is a thick and strong sheet of 
fibers. Often it is considered as identical with the "internal cap- 
sule," the inferior lamina being disregarded. The superior lamina 
ascends fan-like from the crusta to the lateral extremity of the 
corpus callosum with which it intercrosses. It has a free border 
anteriorly, though imbedded in the corpus striatum. Upon its 
internal surface rest the optic thalamus (below and behind), and 
the caudate nucleus (above and further forward), which it thus 
separates from the lenticular nucleus. A bend near the middle 
of the superior lamina, called the genu, divides it into an ante- 
rior and a posterior segment, which tend slightly outward from 
the genu and form an angle with each other, open outward, of 
about 120 degrees. The fibers of the genu are motor. They 
may be traced from the Rolandic area of the cortex through the 
genu of the internal capsule and middle third of the crusta, and 
on down into the spinal cord, where they end in ramifications 
about the cells in the anterior horn of gray matter, From the 



i8 The Brain and Spinal Cord. 

same spinal cells other fibers arise which are distributed chiefly 
to the muscles of the mouth and tongue and of both extremities. 
In the a?iterior segment are fibers from the inner third of the 
crusta which proceed to the prefrontal region of the cerebral cor- 
tex. TYit posterior segment is composed of the "direct sensory" 
tract, which forms the outer third of the crusta. The direct sen- 
sory tract terminates in the occipital lobe. Many fibers of the 
internal capsule give off branches (collaterals) which pass 
through the corpus callosum to the opposite hemisphere; other 
fibers may be traced entire through the same course to the corti- 
cal cells of the opposite side. 

The superior lamina of the internal capsule proceeding up- 
ward and outward into the hemisphere decussates with the corpus 
callosum. Together with the caudate nucleus and optic thala?nus 
(and taenia semicircularis between them), which lie on its internal 
surface, it forms the entire lateral boundary (the beveled surface) 
of the general cavity of the cerebrum. 

Corpus Callosum— The entire roof of the cerebral cavity, rep- 
resenting the base of the wedge,is formed by the corpus callosum. 
A part of the anterior boundary is also formed by it. The corpus 
callosum is a thick sheet of fibers four inches broad, from before 
backward ,jwhich joins the hemispheres together. It constitutes their 
great white commissure, being composed chiefly of those medullated 
axons of the cortical cells which end in arborizations about similar 
cells of the opposite hemisphere. It contains some fibers which,af ter 
passing through it, turn down in'the internal capsule; and, also, col- 
laterals from capsular fibers which run through it to the opposite 
cortex. The corpus callosum is placed nearer to the anterior than 
the posterior pole of the hemispheres. Separating the hemispheres 
above, it is seen in the bottom of the great longitudinal fissure. It 
is about an inch in transverse length. The upper suiface is con- 
cave from side to side; arid divided, mesially, by a longitudinal 
raphe. Transverse striae are plainly visible. A few longitudi- 
nal s trice are also found running on either side of the raphe, the 
nerves of Lancisi ; and others run near the lateral end of the cal- 
losum. At the anterior and at the posterior border the corpus 
callosum is bent downward (scroll-like); hence, it is superiorly 
convex from before backward. 

The posterior border is flexed about twenty degrees. Giving 
passage to the fibers which join the middle and posterior parts of 



The Cerebrum. 19 

the hemispheres, the posterior border is the thickest part of the 
corpus callosum. It is on that account called the pad or 
splenium. 

The anterior border is bent downward and then backward, 
sweeping through 180 degrees of flexion. It terminates in a sharp 
edge (sharp point, seen in sagittal section) called the rostrum. 
The rostrum mesially is continuous with the lamina terminalis at 
the base of the brain. It sends downward on either side a band 
of fibers, continuous with the nerves of Lancisi, which constitute 
the peduncle of the corpus callosum. Each peduncle, after pass- 
ing across the anterior perforated lamina, ends in the uncus of 
the hippocampal gyrus. The transverse fibers of the rostrum, in 
the hemisphere, form the floor of the anterior horn of the lateral 
ventricle. The down-turned part of the corpus callosum is the 
genu. It joins the rostrum to the main part or body. The genu 
forms part of the anterior boundary of the cerebral cavity. Fibers 
uniting the frontal lobes of the cerebrum pass through it, and 
in the hemisphere, bound the anterior horn of the lateral ventri- 
cle above and in front. Those fibers forming the roof of the an- 
terior horn are called the forceps minor. The forceps major, 
composed of fibers from the splenium, lies in the roof of posterior 
horn. The great sheet of fibers which constitutes the body of the 
corpus callosum is called the papetum (the coverlet). 

Each lateral extremity of the corpus callosum is overhung by 
the gyrus fornicatus. The lateral longitudinal striae (taenia 
tecta) are entirely covered by it and it incloses between itself and 
the callosum the fissure-like ventricle of the corpus callosum. 

Disregarding small irregularities, the boundaries of the gen- 
eral cavity of the cerebrum may be given as follows: — 
Roof, (Base of wedge) — 

Corpus callosum. 
Floor, (Edge of wedge) — 

Tegmentum (Mid-brain), 

Posterior perforated lamina (Mid-brain), 

Tuber cinereum, 

Infundibulum, 

Lamina cinerea. 
Lateral wall, (beveled surfaces) — 

Internal capsule, 

Caudate nucleus, 



20 The Brain and Spinal Cord. 

Taenia semicircularis, 
Optic thalamus. 
Anterior wall, (border of wedge) — 
Lamina terminalis, 
Anterior commissure, 
Genu of corpus collosum. 
Posterior wall — 

Corpora quadrigemina (Mid-brain) and 
Posterior commissure (with aqueduct of Sylvius be- 
neath them), 
Pineal body, 

Great transverse fissure, containing the velum interpositum, 
Splenium (being bent down slightly behind the cavity). 
The cerebral cavity thus bounded is subdivided by two parti- 
tions. The body of the fornix (together with the velum interposi- 
tum and roof epithelium of the third ventricle) forms a horizontal 
partition which divides the cavity into an upper and lower 
chamber. The superior chamber is divided into two lateral 
chambers, the lateral ventricles, by a double vertical partition, 
the septum lucidum. The inferior chamber is the third ven= 
tricle. 

The body of the fornix is a triangular sheet of fibers, whose 
base is attached to the under surface of the splenium of the cor- 
pus callosum, and whose bifid apex extends forward to the ros- 
trum and to the anterior commissure. Its lateral borders rest on 
the optic thalami, the velum interpositum alone intervening. 
Thus the narrow chamber between the optic thalami (the third 
ventricle) is separated from the broader, superior part of the 
cerebral cavity by the body of the fornix. The body of the for- 
nix is produced by the approximation of two bundles of white 
fibers, one belonging to each hemisphere. These bundles are the 
pillars of the fornix. 

The posterior pillar may be traced from the uncus (as cor- 
pus fimbriatum), and from the hippocampus major upward 
through the descending horn and into the floor of the body of the 
lateral ventricle, where it unites with its fellow of the opposite 
side in forming the body of the fornix. At the apex of the body 
of the fornix the bundles again separate. 

The anterior pillars, one on either side, pass down in front of 
the optic thalami, bounding the foramina of Monro; and then 



The Cerebrum. 21 

descend to the corpora albicantia, at the base of the brain. On 
the way down the pillars pass behind the anterior commissure, 
beyond which each pierces the inner part of the optic thalamus of 
the same side. The fibers of the anterior pillars probably termi- 
nate in the cells of the corpora albicantia, from which other fibers 
take their origin (the bundles of Vicq d'Azyr) and ascend to the 
anterior nuclei of the optic thalami. 

The upper surface of the body of the fornix is convex from be- 
fore backward. It forms the postero-median part of the floor of 
the lateral ventricle. Mesially, it is joined to the corpus callosum 
by 

The septum lucidum,a double-walled sagittal partition which 
divides the superior chamber of the cerebral cavity into lateral 
halves, the lateral ventricles. The septum lucidum is crescentic 
in outline. Its convex border fits, mesially, into the concave sur- 
face of the body, genu and rostrum of the corpus callosum. Its 
concave border rests upon the fornix. The inferior angle is in 
contact with the anterior commissure between the rostrum and 
anterior pillars of the fornix. Each wall of the septum lucidum 
is a part of the original mesial wall of the cerebral hemisphere 
and is, therefore, composed of cortical and medullary matter. 
The walls inclose a part of the great longitudinal fissure, called 
the fifth ventricle. That fissure, in embryo, was open down to 
the velum interpositum on the inter-brain; but its lower part be- 
comes cut off and inclosed by the development of the fornix, an- 
terior commissure and corpus callosum. The cerebral cavity is 
thus divided into four ventricles, viz. : 

Two lateral (the ventricles of the hemispheres), 

Fifth (the ventricle of the great longitudinal fissure), and 

Third (ventricle of the inter-brain). 

THE FIFTH VENTRICLE. 

This is the fissural ventricle or the ventricle of the septum. 
The fifth ventricle is a very narrow, antero-posterior cleft between 
the walls of the septum lucidum, with which it coincides in ex- 
tent. It is situated between the lateral ventricles, above and 
anterior to the third ventricle. It is not a part of the embryonic 
brain cavity, but of the great longitudinal fissure. Therefore, it 
does not communicate with any other ventricles, all the others 
being a part of the cavity of the neural tube from which both 



22 The Brain and Spinal Cord. 

brain and cord are developed. Instead of ependyma which lines 
other ventricles, the lining of the fifth is modified pia mater. A 
lymph-like fluid fills it. 

THE LATERAL VENTRICLES. 

The hemispheres contain the largest of the six ventricles. Sit- 
uated one on either side of the median line, the ventricles of the 
heniispheres are very naturally called the lateral ventricles. 
Each represents a branch of the cavity of the embryonic neural 
tube, from the walls of which the brain and spinal cord are devel- 
oped. In consequence, the lateral ventricles communicate with 
all others except the fifth. By the foramen of Monro, each 
directly communicates with the third ventricle; and through that, 
indirectly, with the fourth and sixth. The foramen of Monro is 
situated between the front of the optic thalamus and the anterior 
pillar of the fornix. It extends between the anterior extremity of 
the third ventricle and the junction of the anterior horn with the 
body of the lateral ventricle. The lateral ventricles are lined 
with ependyma, which is a transparent membrane composed of 
two layers, viz.: neuroglia, with a covering of columnar ciliated 
epithelial cells. Over the optic thalamus (the part seen in the 
lateral ventricle), and the choroid plexus, the neurogliar layer is 
absent. 

The lateral ventricle may be studied best in four parts: the 
central part or body ; the anterior, the jniddle or descending, and 
the posterior cornu* 

The body of the lateral ventricle is the ventricle of the parie- 
tal lobe of the cerebrum. The following are its boundaries: — 

Roof — Tapetum of corpus callosum. 

Floor — (from before, backward and inward) 

Caudate nucleus of the corpus striatum, 

Taenia semicircularis, 

Optic thalamus (covered by epithelium), 

Choroid plexus (covered by epithelium), 

Fornix. 

Mesial wall — Septum lucidum, 

External wall — Internal capsule. 

The tapetum forms a complete roof tor the body of the lateral 
ventricle. The roof inclines upward and outward from the sep- 
tum lucidum, the inner wall of the ventricle, to the superior lam- 



The Cerebrum. 23 

ina of the internal capsule which forms its outer wall. The floor 
of the body of the ventricle is formed by the five parts, as named 
above, which will now be considered in the order given. 

Corpus striatum — The striated body is the basal ganglion of 
the hemisphere. It is an ovoid mass of gray matter imbedded, for 
the most part, in the cerebral medulla; but it is continuous below 
with the anterior perforated lamina and extends above into the 
floor of the lateral ventricle. It is placed anterior and external to the 
optic thalamus. A few large and very many small multipolar cells, 
with their associated fibers, all bound together by neuroglia, com- 
pose the ganglion. Those cells are pigmented. The streaked 
appearance of the corpus striatum is due to the white capsular 
fibers which pierce it. The internal capsule divides it into two 
nuclei, viz.: the lenticular nucleus (the extraventricular part), 
and the caudate nucleus, which is in relation with the lateral ven- 
tricle. Anterior to the free borders of the superior and the infe- 
rior capsular lamina, the two nuclei are united with each other, 
with the anterior perforated lamina and with the lower end of the 
claustrum. 

The lenticular nucleus occupies the cone-like cavity of the in- 
ternal capsule, by whose laminae it is separated from the ventri- 
cle. It is shorter fore and aft than the caudate nucleus. It re- 
sembles a biconvex lens with a somewhat thickened anterior 
border, when viewed in horizontal section. In transverse vertical 
section through its center it is triangular in shape. The hypotenuse 
and base are formed, respectively, by the superior and inferior 
lamina of the internal capsule. The external capsule forms the 
perpendicular and separates the lenticular nucleus from the claus- 
trum. The latter is a thin sheet of isolated cortical matter, found 
just mesial to the island of Reil. In extent and position, fore and 
aft, the island of Reil and lenticular nucleus coincide. The len- 
ticular nucleus is subdivided by two white la?nino3, parallel with 
its external surface, into three zones. The outer zone, called the 
putamen, is deeply pigmented and, like the caudate nucleus, is of 
a reddish gray color; but the two inner zones, having less pig- 
ment, are of a pale, yellowish tint. They form the globus palli- 
dus. 

More of the large multipolar cells are found in the lenticular 
nucleus than in the caudate. It also receives and gives off many 
fibers. Some of them join it to the caudate nucleus; others pass 



24 The Brain and Spinal Cord. 

directly from the globus pallidus into the superior lamina of the 
internal capsule; and still others, the ansa lenticularis, are re- 
ceived below, from the optic thalamus. Those thalamic fibers which 
pass upward in the medullary laminae are distributed chiefly to 
the middle and outer lenticular zones; but others of them ascend 
between the putamen and the claustrum, and, there, joined by 
fibers from the anterior, commissure, constitute the external cap- 
sule. 

The nucleus caudatus (the tailed nucleus) is a pear-shaped 
body of reddish-gray color, situated on the perimeter of the inter- 
nal capsule. 

It is the intraventricular part of the striated body and forms a 
strip of the ventricular floor along the outer wall. The bulb of 
the caudate nucleus is directed forward. It is seen in the anterior 
horn of the lateral ventricle. From the bulb the nucleus tapers 
as it proceeds .backward through the body of the ventricle. Its 
tail or surcingle turns downward in the roof of the middle horn 
and ends in a considerable swelling, called the amygdala, near 
the apex of that horn. The caudate nucleus is covered on its 
ventricular surface by ependyma. The opposite surface, resting 
against the fibers of the internal capsule, is irregular and 
serrated. 

The taenia semicircularis lies just internal to the nucleus 
caudatus. It is a band of white fibers traversing the floor of the 
body of the ventricle and the roof of its descending horn. It may 
be said to arise from the amygdala. Ascending to the body of the 
ventricle, it passes forward between the caudate nucleus and the 
optic thalamus to the foramen of Monro, where it divides into two 
bundles. One of them joins the interior pillar of the fornix. The 
other, passing over the anterior commissure, terminates in front of 
it in a mass of cells between the septum lucidum and the nucleus 
caudatus. Perhaps some fibers terminate in the latter. 

Optic thalamus — A fusiform part of this ganglion of the inter - 
brain is visible in the floor of the literal ventricle between the 
taenia semicircularis and the choroid plexus. It extends through- 
out the ventricular body from the foramen of Monro to the de- 
scending horn. A transparent layer of epithelium, extending 
from the fornix to the taenia semicircularis, and representing the 
hemisphere wall, covers it. The optic thalamus will be described 
with the third ventricle and inter-brain. 



The Cerebrum. 25 

The choroid plexus of the lateral ventricle is the vascular bor- 
der of the velum interpositum. It projects laterally from beneath 
the fornix and its posterior pillar into the floor of the body of the 
ventricle and the inner wall of the descending horn. The epithe- 
lium, above mentioned, invests it; and it borders the fornix like a 
ruffle. It is called "choroid" plexus ixplov, a membrane) because it 
is membrane-like. The anterior choroid artery from the internal 
carotid and the posterior choroid, a branch of the posterior cere- 
bral, supply the plexus. The former pierces the temporal lobe 
and enters the apex of the descending horn of the ventricle; the 
latter passes in through the great transverse fissure, following the 
velum interpositum. The choroid vein carries the blood away. 
At the foramen of Monro, it is joined by the vein of the striated 
body and forms the vein of Galen. The vein of Galen courses 
backward in the velum interpositum and unites with its fellow of 
the opposite side and then the common vein uniting with the in- 
ferior longitudinal sinus, forms the straight sinus. 

The floor of the body of the lateral ventricle is completed by 
the superior surface of the fornix. 

The Cornua of the Lateral Ventricle are three in number. 
The anterior cornu projects from the body of the ventricle for- 
ward and outward around the bulb of the caudate nucleus. It is 
the ventricle of the frontal lobe and is deep and narrow. Its 
boundaries are as follows: — 

Roof — Corpus callosum (forceps minor). 

Floor — Rostrum. 

Anterior wall — Genu. 

Inner wall — Septum lucidum. 

Outer wall — Caudate nucleus. 
The posterior cornu is directed backward in a curve, concave 
inward, from the ventricular body into the occipital lobe. Its ex- 
tremity bends mesially toward the calcarine fissure with which 
the horn is parallel. Th\t fissure produces the ridge along the 
inner wall called the hippocampus minor. The posterior horn 
is roofed over by fibers from the splenium of the corpus callosum, 
which turn down outside the horn and also form part of the ex- 
ternal boundary. A well-marked bundle of fibers from the 
splenium, forceps major, is found passing along the mesial border 
of the roof into the occipital lobe. The white matter of the occipi- 
tal lobe forms the remaining boundaries. The anterior extremity 



26 The Brain and Spinal Cord. 

of the posterior cornu is continuous, laterally, with the beginning 
of the descending horn. At the junction of the two is a triangular 
area, the trigonum ventriculi. 

The middle or descending cornu is the ventricle of the tem- 
poral lobe. Its course is crescentic as it follows the perimeter 
of the internal capsule. It first runs outward and backward from 
the body of the ventricle, then it turns downward, and finally it 
proceeds forward and inward to within an inch of the apex of the 
temporal lobe. In horizontal section just below the general cavity 
of the ventricle, the descending horn is triangular. In that posi- 
tion it has a posterior wall (or floor), an inner wall and a curved 
antero-zxternal wall (or roof), which is continuous above with the 
outer wall and floor of the body of the ventricle. 

The parts found in the walls of the descending cornu may be 
enumerated as follows: 

Roof (or antero-external wall) — 

Corpus callosum (at the junction of horn and body), 
Pulvinar of optic thalamus (covered by epithelium), 
Inferior lamina of internal capsule, partially covered by 
Surcingle and amygdala of caudate nucleus, and 
Taenia semicircularis. 
Floor (or posterior wall) — 

Hippocampus major and pes hippocampi, 
Eminentia collaterals, 

Posterior pillar of fornix and corpus fimbriatum. 
Inner wall (mesial) — 

Epithelium (of hemisphere wall) covering, 
Pulvinar, 
Choroid plexus, 
Transverse fissure, and 
Dentate fascia. 
The structures in the roof of the descending horn have been 
sufficiently described. They are easily understood when it is re- 
called that the roof of the horn is continuous with the outer wall 
and floor of the central cavity of the ventricle. 

Throughout the floor of the middle horn is a prominent ridge, 
the hippocampus major, which enlarges downward to alobulated 
extremity called the pes hippocampi. The ridge is due to the 
infolding of the floor over the hippocampal fissure on the mesial 
surface of the cerebrum. The ventricular surface of the hippo- 



The Cerebrum. 27 

campus major is formed by a lamina of white matter, the alveus, 
but the deeper part is cortical matter composed almost entirely of 
large pyramidal cells. External to the upper end of the hippo- 
campus is a low ridge caused by the collateral fissure. It is the 
eminentia collateralis. The posterior pillar of the fornix rests 
in the concavity of the hippocampus, where most of its fibers ter- 
minate, but a small bundle of them, the corpus fimbriatmn, passes 
beyond it and ends in the uncus. 

A I xyer of epithelium representing the hemisphere wall forms 
the whole inner wall of the descending cornu. Superiorly, it 
covers the cushion-like projection (the pulvinar) of the optic 
thalamus, which forms a small part of both roof and inner wall. 
Behind, it is attached to the pillar of the fornix, from which it 
extends forward to the taenia semicircularis. The epithelium 
covers the transverse fissure which otherwise would form a com- 
munication between the horn and the exterior. Through the 
transverse fissure the border of the velum interpositum projects; 
and, pushing the epithelium before it into the horn, forms the 
choroid plexus. Within the fissure there is a serrated free border 
of cortex called the dentate fascia. The dentate fascia folds 
mesially in front of the hippocampal fissure and with the hippo- 
campus major forms an S -shaped fold of the cortex. The S-shape 
is perfect in the lefc hemisphere when viewed with the frontal 
lobes upward and the convex surface of the bram toward the 
spectator. The top of the letter is the fascia dentata; the supe- 
rior curve is the hippocampus, produced by the hippocampal 
fissure, the upper concavity; the lower concavity, open toward the 
ventricle, is the groove between the hippocampus major and the 
eminentia collateralis. 

THE THIRD VENTRICLE AND INTER-BRAIN. 

The inter-brain is mesial in position. It is situated beneath 
the fornix and the layer of epithelium extending from the border 
of the fornix to the taenia semi-circularis. The velum interpos- 
itum only intervenes between them. The ventricle of the inter- 
brain is the third in number, The third ventricle, therefore, 
is mesially located; and is at a lower level than the ventricles of 
the hemispheres. Through the foramina of Monro its anterior part 
communicates with each lateral ventricle, and the aqueduct of 
Sylvius connects it, behind, with the fourth ventricle. The third 



28 The Brain and Spinal Cord. 

ventricle is fissure-like. It is a very narrow vertical cleft about 
an inch in length from before backward, which separates the optic 
thalami and extends almost to the inferior surface of the cerebrum. 
The roof follows the curve of the fornix and arches from the pos- 
terior commissure forward to the anterior commissure. The 
anterior wall extends from the upper border of the anterior com- 
missure down to the optic recess at the angle of flexion of the 
lamina cinerea. The floor describes two arches, convex toward 
the ventricle, The first arch, very convex, stretches between the 
optic recess and the infundibulum in which the floor reaches its 
lowest point. The distance from the infundibulum to the anterior 
orifice of the aqueduct of Sylvius, is spanned by the second arch. 
It is rather flat. Its posterior extremity is but a sixteenth of an 
inch below the posterior commissure; the anterior orifice of the 
Sylvian aqueduct separates them. The ventricle is thus contracted 
behind to the size of the Sylvian aqueduct with which it is contin- 
uous. The lateral walls are close together throughout. At one 
point near the middle they come together and are joined by the 
gray or middle commissure. Antero-superiorly the lateral wall 
is perforated by the foramen of Monro. The foramen constitutes 
the slight separation between the front of the optic thalamus and 
the anterior pillar of the fornix. It opens into the lateral ven- 
tricle at the junction of the anterior horn with -the body. The 
epeiidyma which lines the third ventricle is continuous through the 
foramen of Monro with the lining of the lateral ventricle. But 
one layer of the ependyma is present in the roof of the ventricle 
and that is the epithelial layer. The third ventricle is occupied 
by cerebro-spinal fluid. 

The following are the boundaries of the third ventricle: 

Roof- 
Posterior commissure, 
Roof epithelium and pmeal body, 
Velum interpositum and choroid. plexuses, 
Fornix. 

Anterior wall — 

Epithelium, covering 

Pillars of fornix and anterior commissure. 
Lamina terminalis. 



The Cerebrum. 29 

Floor — 

Lamina cinerea and optie commissure, 
Tuber cinereum and infundibulum, 
Corpora albicantia, 

Posterior perforated lamina (of mid-brain), 
Tegmentum (of mid-brain). 

Posteriorly — 

Ventricle is continuous with aqueduct of Sylvius. 

Lateral walls — 

Optic thalamus, 

Anterior pillar of the fornix, and 
Foramen of Monro between them. 

Posterior commissure— A band of white fibers passes ; across 
the back part of the third ventricle and supports the posterior end 
of the roof epithelium. That is the posterior commissure. It 
crosses immediately in front of the corpora quadrigemina. Be- 
neath it, is the anterior orifice of the aqueduct of Sylvius. The 
pineal body is above and behind it, and it is enclosed between 
the ventral and dorsal pineal laminae. The posterior commissure 
stretches from one optic thalamus to the other; but most of its 
fibers terminate in the parieto-occipital region. It contains four 
sets of fibers, viz.: (1) Commissural fibers between the optic thai- 
ami; (2) the upper decussation of the posterior longitudinal bun- 
dles; (3) some fibers from the pineal stria, derived from the optic 
tract near the external geniculate body, which cross to the oppo- 
site nucleus (upper part) of the motor oculi (Darkschewitsch); 
and, (4) fibers from superior quadrigeminal body to the opposite 
hemisphere. 

The roof epithelium of the third ventricle stretches from the 
posterior commissure to the anterior commissure and, laterally, is 
attached to the upper internal border of the optic thalamus. It is 
the superficial layer of the ependyma which lines the ventricle; 
but it is, here, the only adult representative of the roof of the 
neural tube (the thalamencephalon). Anteriorly, this same 
epithelium investing the anterior commissure and pillars of the 
fornix, is the only representative of the neural wail (prosencepha- 
lon) down to the lamina terminalis. The roof epithelium presents 
two longitudinal folds suspended in the ventricle. The lower 



30 The Brain and Spinal Cord. 

layer of the velum interpositum invests it superiorly, anterior 
choroid tela ; and, dipping- down into its folds, forms the choroid 
plexuses of the third ventricle, which communicate with those of 
the lateral ventricles through the foramina of Monro. At the back 
part in the middle line, there is a pouch-like evagination of the 
roof epithelium, which develops into the pineal body. 

Pineal body or conarium— It is a cone shaped body, a quar- 
ter of an inch high and one-sixth of an inch in diameter, joined to 
the roof of the third ventricle by a flattened stalk or peduncle. 
It is situated in the floor of the great transverse fissure, directly 
below the splenium of the corpus callosum, and rests between 
the superior quadrigeminal bodies on the dorsal surface of the 
mid-brain. It is closely invested by pia mater. The pineal 
stalk splits into a dorsal and a. ventral lamiaa. The ventral 
lamma, passing behind the posterior commissure, disappears be- 
neath it; but the dorsal stretches forward over the commissure in 
continuity with the roof epithelium. The borders of the dorsal 
lamina are thickened, pineal stria or habenulce, and contain 
fibers which, running forward, join the anterior pillar of the for- 
nix. The pineal striae also contain optic fibers which pass 
through the posterior commissure to the nucleus of the oculomo- 
tor nerve. 

The interior of the pineal body is made up of closed follicles 
surrounded by in growths of connective tissue. The follicles are 
filled with epithelial cells mixed with calcarious matter, the 
brain-sand (acervulus cerebri). Calcarious deposits are found 
also on the pineal stalk and along the choroid plexuses. The 
function of the pineal body is unknown. It is supposed to repre- 
sent a cyclopian eye or a heat organ of certain invertebrate rep- 
tiles long extinct. 

The velum interpositum, a double triangular fold of pia 
mater, is interposed between the roof of the third ventricle and 
the mesial part of the floor of the two lateral ventricles. Its apex 
is just behind the anterior commissure, and its base, directed 
backward, is continuous, by the upper layer, with the pia of the 
occipital lobes; and, by the inferior layer, it is continuous with 
the pia on the dorsal surface of the mid-brain and cerebellum. 
Each border constitutes the choroid plexus of the lateral ventri- 
cle, which is seen (through the epithelium) in the floor of the 
body and along the inner wall of the descending horn. Mesially, 



The Cerebrum. 31 

the inferior lamina of the velum interpositum invests the roof ep- 
ithelium of the third ventricle, forming- the anterior or superior 
choroid tela ; and, laterally, it covers the median half of the upper 
surface of the optic thalami. It forms the two choroid plexusesoi the 
third, or inter-brain, ventricle. Between the inferior and supe- 
rior lamina is inclosed some arachnoid tissue; and the veins of 
Galen pass back through it from the foramina of Monro to the 
tentorium cerebelli where they join with the inferior longitudinal 
sinus in forming the straight sinus. 

The anterior commissure is a very distinct round bundle of 
white fibers. It is seen in the anterior wall of the third ventricle 
supporting the roof epithelium. The epithelium there bends 
down between the pillars of the fornix and invests the ventricu- 
lar surface of the commissure. The anterior commissure rests 
upon the upper extremity of the lamina terminalis, between the 
pillars of the fornix behind and the rostrum of the corpus callosum 
in front. With the last two structures it is developed from the 
hemisphere vesicles. It is the most important connecting link 
between the hemispheres in vertebrates without a corpus callo- 
sum (all below mammals). It contains two groups of fibers: — (1) 
the pars temporalis, by far the larger groop, pierces the globus 
pallidus of the lenticular nucleus, unites with the ansa lenticu- 
laris in forming the external capsule, and then ends in the tem- 
poral cortex. It is che commissure of the temporal lobes. And, 
(2) the pars olfactoria in which fibers pass from the olfactory 
tract to the opposite hippocampal convolution. 

The up-turned part of the lamina cinerea, extending from the 
commissure and rostrum down to the angle which incloses the 
optic recess, completes the anterior boundary of the third ven- 
tricle. 

The floor is very narrow. It is formed by the interpeduncular 
structures, plus the tegmentum, namely: lamina cinerea (with 
optic chiasma below it), tuber cinereum and infundibulum, cor- 
pora albicantia, posterior perforated lamina (a part of the sub- 
stantia nigra), and the tegmentum. The last two are the middle 
and dorsal portions of the mid-brain; the others belong to the 
inter-brain, and all extend laterally beneath the optic thalami. 
The corpora albicantia, located on either side of the mesial line, 
may be excepted from the ventricular floor; as they are directly 
beneath the thalami. (See base of cerebrum). 



32 The Brain and Spinal Cord. 

The third ventricle has its lateral wall formed by the optic 
thalamus and the anterior pillar of the fornix. The pillar of the 
fornix, diverging from its fellow, proceeds downward and back- 
ward to the corpus albicans through the mesial part of the thala- 
mus. In the ventricle it is covered by the epeudymal epithelium. 
It bounds the foramen of Monro in front. 

Optic Thalamus — It is the great ganglion of the inter-brain. 
The third ventricle separates it from its fellow, except at the mid- 
point where they are joined by the middle (gray) commissure. It 
is situated behind and mesial to the corpus striatum and projects 
backward over the superior surface of the mid-brai n. Laterally, 
it rests against the superior lamina of the internal capsule, which 
separates it from the lenticular nucleus. The. optic thalamus is 
shaped like an egg with the small end directed forward. It has 
an anterior and posterior extremity and four surfaces: superior, 
inferior, internal and external. 

Extremities — The anterior extremity is lost in a large group 
of fibers (anterior stalk) which ends in the frontal lobe of the cere- 
brum. 

The posterior end presents a large prominence (cushion-like), 
the pulvinar ; and beneath it a smaller swelling which is the 
external geniculate body. The internal geniculate body (of the 
mid-brain) is also continuous with this extremity internal to the 
pulvinar. 

Surfaces— The internal, or mesial surface forms the lateral 
wall of the third ventricle. It is joined to the opposite internal 
surface by the middle commissure. Both this and the superior 
surface are composed of a thin lamina of longitudinal white fibers 
(the stratum zonale). 

The superior surface of the thalamus is divided by an oblique 
groove, corresponding in position to the border of the fornix, into 
two areas. The area inside the groove is covered by the velum 
interpositum and the fornix. It is elevated in front, forming the 
a7iterior tubercle. Internally it i5 bound by the pineal stria and 
attachment of the roof epithelium. Posteriorly, next the stria 
(habenula) is a triangular depression bounded behind by a trans- 
verse groove in front of the corpora quadrigemina; and by a 
slight groove, the sulcus habenuke, externally. That depressed 
surface is called the trigo?ie of the habenula. Beneath the tri- 
angle is one of the thalmic nuclei. The outer area is seen in the 



The Cerebrum. 33 

floor of the lateral ventricle. The sheet of epithelium between 
the fornix and taenia semicircularis separates it from the cavity. 

External Surface— A special lamina of fibers, the external 
medullary lamina derived from the superior fillet, forms the ex- 
ternal surface of the optic thalamus. 

The inferior surface blends with the superior surface of the 
tegmentum and substantia nigra and forms the laminae and nuclei 
of the subthalmic tegmental region. (See below.) 

The interior of the optic thalamus is made up chiefly of 
gray matter containing multipolar and fusiform cells. The 
white matter, the internal medullary lamina, divides the gray 
into four nuclei, 

(1) The internal nucleus is joined to the opposite inner nu- 
cleus by the gray (or middle) commissure and is continuous with 
the gray matter in the wall and floor of the third ventricle; but 
the internal medullary lamina separates it from the other nuclei 
of the same thalamus. 

(2) The external nucleus is the largest. It extends into the 
pulvinar. From it many fibers pass into the internal capsule. 

(3) The nucleus of the anterior tubercle (or anterior nu- 
cleus) appears to give origin to the fibers forming the bundle of 
Vicq d'Azyr. 

(4) The posterior nucleus (or nucleus of the habenula) lies be- 
neath the trigonum habenulae. It receives fibers from the pineal 
stria and originates a bundle of fibers (fasiculus retroflexus, Mey- 
nert), which may be traced back through the tegmentum to the 
interpeduncular ganglion (at the divergence of the crustae) in the 
substantia nigra. The anterior and posterior nuclei are small in 
comparison with the internal and external. 

The white matter of the optic thalmus has, for the most part, 
an indefinite arrangement. It forms the S-shaped internal 
medullary lamina and is continued in numerous bundles of fibers 
which enter the hemisphere. The connection of the fibers with 
the cells is not understood. These bundles are as follows: 

(1) The anterior pillar of the fornix (having pierced the 
thalamus) and the bundle of Vicq d'Azyr descend from the 
inferior surface to the corpus albicans. 

(2) A few fibers in the middle and posterior commissures join 
the mesial surfaces. 

(3) From the external surface two groups proceed into the 



34 The Brain and Spinal Cord. 

tempero-parietal region,— (a) the inferior (ansa peduncularis 
passes below the lenticular nucleus with the internal capsule to 
the temporal lobe, (but some of its fibers enter into the external 
capsule); and, (b) the superior group (ansa lenticularis), which 
pierces the superior lamina of internal capsule and is distributed 
to the nucleus lenticularis and parietal cortex. The latter also 
helps to form the external capsule. 

(4) The anterior stalk streams from the anterior end of the 
thalamus into the frontal lobe; and, 

(5) A large pencil of fibers, the optic radiatio7is> pass from the 
pulvinar to the visual centers in the occipital lobe. The last 
group is in part a continuation of the outer root of the optic tract. 

Subthalmic tegmental region is composed of three layers: 
(i) Stratum dorsale (next the optic thalamus); (2) Zona incerta 
(middle); and (3) the nucleus of Luys or subthalmic body 
(inferior). The nucleus of Litys is but the terminal part of the 
substantia nigra. The reticular formation of the tegmentum, 
continuing beneath the optic thalamus, forms the zona incerta. 
The stratum dorsale is made up as follows: (a) Fibers from the 
posterior longitudinal bundle (Meynert); (b) the superior pe- 
duncle of cerebellum (Forel) among which is the upper end of 
the red nucleus of the tegmentum; and (c) upper fillet 
(Wernicke). 

The external geniculate body (geniculum, a little knot or 
knee) forms a slight swelling beneath the pulvinar on the pos- 
terior end of the optic thalamus. It marks the apparent end of 
the outer root of the optic trace and gives rise to some of its 
fibers. It is joined to the anterior quadrigeminal body by the 
anterior brachium. In appearance, it is dark colored and lami- 
nated; its gray matter, which contains pigmented multipolar 
cells, is divided into thick layers by thin laminse of fibers from 
the optic tract. The processes of the multipolar cells help to 
form the optic radiations. 

The internal geniculate body belongs to the mid-brain. It is 
placed at the end of the inner root, as the external geniculate is 
at the end of the outer root, of the optic tract. It rises up from 
the groove between the optic thalamus and corpora quadri- 
gemina, and is joined to the posterior quadrigeminal body by the 
posterior brachium. The anterior brachium sweeps around it, in 
front and externally, passing between it and the external genie- 



The Cerebrum. 35 

ulate body. The internal geniculate body is gray in color and is 
not laminated. Its cells are small, and fusiform in shape. They 
perhaps give origin to the intercerebral fibers (Gudden) of the 
optic tract. 



MID-BRAIN. 



Th? brain just behind the cerebrum is the mid-brain. It is the 
connecting link between the inter-brain and the hemispheres in 
front and the pons behind. This has suggested the name isthmus, 
sometimes applied to it. It is developed from the middle of the 
five brain-vesicles, the mesencephalon. The cerebral hemi- 
spheres almost conceal it from view; they overhang it dorsally, 
and the temporal lobes, inclosing it between them, bend mesially 
and cover part of its ventral surface. Only the median part of 
the ventral surface is visible in the complete brain. The form of 
the mid-brain resembles a flattened cylinder. Its axis, a half an 
inch long, is pointed upward and forward, and its long diameter, 
which varies from an inch to an inch and a quarter in length is 
directed transversely. 

SURFACES. 

It has four surfaces, viz., the ventral and dorsal which are free, 
and the superior and inferior, representing the ends of the cylin- 
der, which are attached. The two latter are parallel with each 
other. 

The superior surface, sloping downward and forward, meets 
the ventral surface at an acute angle. Its inclination is that of 
the back part of trie floor of the third ventricle. External to the 
floor of the ventricle it is attached to the optic thalami and inter- 
nal capsules. The blending of it with the thalami forms the sub- 
thalmie tegmental regions, and the continuations of the extreme 
lateral portions, the crustae, constitute the internal capsules of the 
hemispheres. In the median line behind the third ventricle, it is 
attached to the posterior commissure. 

The inferior surface joins the upper surface of the pons. It 
is a little narrower than the superior surface. It is about one 
inch broad and three-quarters of an inch dorso-ventrally. 

The ventral surface of the mid brain looks downwaid and 
forward. It is deeply grooved longitudinally by the mesial 

36 



Mid-Brain. 37 

sulcus and is slightly concave from above downward. It is sepa- 
rated on either side from the dorsal surface by the sulcus lateralis. 
Though partially concealed by the temporal lobes of the cere- 
brum, the ventral surface is unattached. It is formed by a prom- 
inent band, the crusta, at either side, and the posterior perforated 
lamina, which is inclosed between them. The latter forms the 
floor of the mesial sulcus. The inner border of the crusta is free 
and overhangs the perforated lamina slightly. Thus is formed 
the oculomotor groove (between the crusta and perforated 
lamina) whence the third cranial nerve takes its superficial ori- 
gin. The fourth nerve courses forward over the ventral surface, 
but is not attached to it. 

The dorsal surface of the mid-brain, though free, is entirely 
concealed by the cerebral hemispheres. It forms part of the 
floor of the great transverse fissure and is covered by pia mater. 
The lateral sulcus bounds it on each side. From the sulcus 
lateralis it elevates abruptly toward the median line where it 
presents a longitudinal groove. This produces two ridges which 
are subdivided by a transverse groeve into the four eminences of 
the corpora quadrigemina. On either side, anterior and a little 
external to the quadrigeminal bodies, is the internal geniculate 
body. There are thus presented six eminences on the dorsal 
surface of the mid-brain. It is formed by the tegmentum. 

INTERIOR. 

The Mid-brain is made up of three great divisions, viz.: 
(1) The ventral part, composed of the two crusta ; (2) the sub- 
stantia nigra, which is the middle part, and (3) the dorsal part, 
the tegmentum, composed of lateral halves united by a raphe. 

The Crustae are two rounded bands of white fibers, limited by 
the mesial and the lateral sulci, which form the ventral part of 
the mid-brain. They are in contact at the front of the pons from 
which they diverge upward and forward and pierce the inferior 
surface of the cerebrum beneath the optic tracts. Entering the 
cerebrum just external to the optic thalamus, the fibers of each 
crusta spread out, fan-like, in the internal capsule. Excepting 
the mesial fillet, which enters the inferior lamina, the crusta forms 
only the superior lamina of that inner capsule. The crustae are 
also called peduncles and crura. They contain three groups of 
fibers. 



38 The Brain and Spinal Cord. 

(i) The "direct sensory tract" forms the outer third of each 
crusta. Its fibers may be traced from the nuclei pontis ( ?) through 
the posterior segment of the superior lamina of the internal cap- 
sule to the occipital region of the cerebrum. 

(2) The middle third of the crusta is for the most part motor. 
Its fibers arise in the Rolandic area of the cerebral cortex; they 
form the genu of the inner capsule, the ventral longitudinal fibers 
of the pons and the pyramids of the medulla. Below the medulla 
they are continued in the direct and crossed pyramidal tracts of 
the spinal cord. With the pyramidal fibers of the "middle third' 
are a few from the cerebellum. The cerebellar fibers, upon reach- 
ing the pons through the middle peduncle of the cerebellum, as- 
cend with the ventral longitudinal fibers of the pons and are 
sparsely scattered throughout the crusta. 

(3) The inner third of the crusta is composed chiefly of short 
fibers whose origin is probably the substantia nigra. They form 
the anterior segment of the upper lamina of the internal capsule. 
Their termination is in the prefrontal cortex. The mesial fillet 
exists as a distinct bundle in this part of the crusta . Superiorly 
it bends outward into the subthalmic region and joins the ansa 
lenticularis. It forms a part of the inferior lamina of the internal 
capsule; and, then, of the medullary laminae of the lenticular 
nucleus. The mesial fillet is said by Spitzka to be the afferent 
cerebral tract of the cranial nerves. 

The Substantia Nigra— The central part of the mid-brain is 
a sheet of pigmented gray matter. The substantia nigra is 
visible at the base of the brain between the crustae, the posterior 
perforated lamina, and its margin comes to the surface in each 
lateral sulcus. Antero-posteriorly it extends from the pons, for- 
ward to the corpora albicantia, and nucleus of Luys. Dorsal to it 
is the tegmentum. Transversely, the substantia nigra is convex 
downward, but it is slightly concave longitudinally. The third 
nerve pierces it and comes out through the oculomotor groove. 
It contains small pigmented multipolar cells, which are believed 
to originate the fibers of the inner third of the crusta. There is an 
aggregation of these cells located, mesially, just in front of the 
pons, the interpeduncular ganglion. According to Forel this gan- 
glion receives a bundles of fibers from the nucleus habenulae of 
the optic thalamus. The antero-lateral portion of the substantia 



Mid-Brain. 39 

nigra forms the nucleus of Luys or corpus subthalmicum, on 

either side. 

The tegmentum— The dorsal division of the mid-brain, being 
the largest and covering the other two divisions, is in consequence 
called the tegmentum (the cover). It fits, ventrally, into the con- 
cavity of the substantia nigra, and is bounded by the lateral sul- 
cus on each side. Dorsally it presents the internal geniculate 
bodies and the corpora quadrigemina. The tegmentum is very 
thick mesially. In transverse section it has a pentagonal form, 
the curve of the substantia nigra representing two sides. Superi- 
orly, the anterior extremity of the tegmentum blends with the op- 
tic thalamus in the subthalmic tegmental region. The tegmentum 
is continuous with the pons behind (caudalward). It contains the 
cavity of the mid-brain. 

The aqueduct of Sylvius— Th? aqueduct is a very slender 
canal connecting the third and fourth ventricles. So it is the "iter 
a tertia ad quartum ventriculum." It is situated near the dorsal 
surface of the tegmentum directly beneath the sulcus longitudi- 
nalis. It is half an inch long. In shape it is V-like above; el- 
liptical in the middle, with the major axis vertical; and T-form 
below, where it joins the fourth ventricle. Its height varies be- 
tween a sixteenth and an eighth of an inch. Like other ventricles, 
it is lined with ependyma. A layer of gray matter y thickest on the 
sides and floor, surrounds the aqueduct of Sylvius. It is continu- 
ous with the gray matter of the fourth ventricle. In it are the 

Nuclei of the third and fourth cranial nerves — Both nuclei ex- 
tend the entire length of the aqueduct, and the third is prolonged 
into the wall of the third ventricle, where it receives a bundle of 
fibres from the opposite pineal stria and optic tract. The nuclei 
are composed of several elongated masses of gray matter, which 
contain ganglion cells of various sizes, and they lie side by side in 
each half of the floor of the aqueduct. The third is next the me- 
dian line, and behind unites with its fellow across it. For the 
most part, the third nerve (motor oculi) arises from the nucleus of 
the same side; but it also contains crossed fibers from the posterior 
part of the opposite nucleus and from the posterior longitudinal 
bundle of the opposite side. Some of the last are derived from 
the nucleus of the abducens (sixth nerve) and after crossing to the 
third nerve, help it to supply the internal rectus of one eye-ball; 
while the sixth, arising from the same nucleus, supplies the exter- 



40 The Brain and Spinal Cord. 

nal rectus of the other eye. Thus is conjugate deviation accounted 
for. The third nerve passes djwn to the oculomotor groove 
through tegmentum and the substantia nigra. The root fibers of 
the fourth nerve (patheticus) proceed dorsally and caudalward 
from the nucleus. They decussate with the fibers from the oppo- 
site nucleus in the superior medullary velum (the valve of Vieus- 
sens), from which they emerge on either side of the frenulum. 
They then continue in the opposite nerve around the side and 
over the ventral surface of the mid-brain. 

Fibers of the Tegmentum— The tegmentum is the continuation 
of the dorsal longitudinal fibers and the formatio reticularis of the 
pons, and of the gray matter of the fourth ventricle; and, in addi- 
tion, has the geniculate and quadrigeminal ganglia forming its 
dorsal portion. It is composed of symmetrical halves united by a 
median raphe. Each half contains innumerable transverse and 
longitudinal fibers. Intersecting the many transverse fibers 
are four distinct bundles of longitudinal fibers. They are con- 
tinued up through the pons, from the cerebellum and the me- 
dulla. Those four bundles are as follows: 

(i) The posterior longitudinal bundle lies beside the raphe, 
just ventral to the gray matter of the Sylvian aqueduct. It is 
traceable from the anterior column (Gray) of the spinal cord and 
receives fibers in the pons from the cerebellum and nucleus of the 
sixth nerve. Through the raphe it partially decussates with its 
fellow (lower decussation). Most of it passes into the opposite 
third and fourth cranial nerves. The remainder, decussating 
thiough the posterior commissure (upper decussation) ends in 
the pineal body and stratum dorsale of the subthalmic region. It 
connects the cerebellum with opposite nuclei of the cranial nerves 
and the latter with each other. 

(2) The Fillet — Near the upper end of the pons in the ventral 
part of the formatio reticularis, the fillet forms a very broad band 
of fibers on either side ot the median raphe. The fillet is equal in 
width to half the transverse diameter of the mid-brain. It con- 
tinues into the ventral portion of the tegmentum, but immedi- 
ately divides into three funiculi, viz., a mesial, the mesial fillet, a 
lateral — the lower fillet, and an intermediate bundle — the upper 
fillet. Origin— The fillet is composed of ascending, crossed 
fibers (axons) which arises chiefly in the nucleus gracilis and 
nucleus cuneatus of the medulla; but, in part, from the posterior 



Mid-Braix. 41 

gray comic of the spinal cord and the ventral auditory nucleus. 
The fillet also contains a few fibers from the middle peduncle of 
the cerebellum. The bulbar fibers, from the gracile and cune- 
ate nuclei, decussate in the medulla oblongata (sensory decussa- 
tion); the spinal fibers, from the posterior cornu of gray matter, 
cross in succession beneath the anterior median fissure of the 
cord (in the white commissure) and ascend in the antero-lateral 
column of the spinal cord to join the bulbar fibers in the 
medulla; and these are joined by the auditory fibers, which cross 
over in the pons through the trapezium from the opposite ventral 
auditory nucleus. After the triple division of the fillet, the lower 
fillet is reinforced in the mid-brain by a smalhbundle of fibers 
from the ascending antero-lateral cerebellar tract of the same 
side. 

The lower fillet (or lateral bundle} forms an oblique ridge on 
the dorsum of the tegmentum. It trends upward and inward, 
over the superior cerebellar peduncle, to the posterior quadri- 
geminal body, where its fibers terminate. Ic contains fibers from 
the three origins of the fillet, besides the small bundle from the 
ascending antero-lateral cerebellar tract. The lower fillet prob- 
ably contains all the fillet fibers from the ventral auditory nu- 
cleus. It is thus that the posterior corpus quadrigeminum is 
connected to the eighth, or auditory nerve. 

The mesial fillet (the mesial bundle) runs next the median 
raphe. It bends ventrally through the substantia nigra to the 
inner third of the crusta. Ascending with the crusta to the sub- 
thalmic region, it joins the ansa lenticularis and with it enters the 
medullary laminae of the lenticular nucleus. 

Upper fillet (or intermediate bundle). It flexes dorsally in 
the tegmentum toward the anterior (or superior) quadrigeminal 
body, and a number of its fibers terminate in the tegmental gray 
matter along its course (Edinger and Forel). The greater part of 
the upper fillet terminates in the anterior quadrigeminal body, but 
a small bundle of fibers continues upward through the internal 
capsule to the parieto-occipital cortex of the cerebrum. The 
upper fillet contains bulbar and spinal fibers and also fibers from 
the cerebellum. 

The upper and lower fillets and fibers from the valve of 
Vieussens form a sheet of white matter beneath the corpora 
quadrigemina, called the quadrigeminal lamina. 



42 The Brain and Spinal Cord. 

(3) The superior peduncle of the cerebellum continues 
upward from the dorsal surface ot the pons. It forms a ridge 
near the median line of the mid-brain which ends in front at the 
inferior corpus quadrigeminum. The lower fillet winds inward 
over its anterior extremity. It is joined to its fellow by a sheet 
of white matter, the valve of Vieussens. The fibers of the cere- 
bellar peduncles bend ventrally beneath the corpora quadrigem- 
ina and then, for the most part, decussate (inferior to the iter) 
through the raphe. These crossed fibers with the few uncrossed 
run forward into the inferior surface of the optic thalamus where 
they inclose the red nucleus and help to form the stratum dorsale 
(Forel). Some of the direct fibers terminate in the red nucleus 
and from it others arise and proceed forward toward the thalamus. 

(4) The olivary funiculus— This is the last of the distinct 
bundles of longitudinal fibers in the tegmentum. There are 
other fibers innumerable but they are classified no farther than 
by the term "formatio reticularis." The olivary funiculus 
arises from the olivary body in the medulla. It runs through the 
tegmentum and internal capsule to the cerebral cortex. 

The corpora quadrigemina are four bodies which stand upon 
the quadrigeminal lamina of the tegmentum. They are seen in 
the floor of the great transverse fissure, invested by pia mater and 
overhung, anteriorly by the pineal body. The crucial groove 
separates them and marks out a larger anterior pair, elongated 
from before backward, and a hemispherical posterior pair. The 
internal geniculate body lies in front and a little external to the 
corpora quadrigemina. A ridge made up of white fibers, the 
anterior brachium, joins each anterior quadrigeminal body to the 
corresponding external geniculate body and outer root of the 
optic tract. The anterior brachium half encircles the internal 
geniculate body, sweeping around it in front and externally. 
The posterior brachium forms an oblique ridge between the 
posterior quadrigeminal body and the corpus geniculatum 
internum of the same side. The superior peduncle of the cere- 
bellum and lower fillet form two ridges which end at the back of 
each posterior quadrigeminal body. 

Structure — The corpora quadrigemina are composed chiefly 
of gray matter. The upper and lower fillet and the valve of 
Vieussens form a layer of fibers, the quadrigeininal lamina, upon 
which they rest and which separates them from the gray matter 



Cerebrum and Mid-Brain. 43 

around the aqueduct of Sylvius. They also contain many fibers 
in their interior and are covered, superficially, by a thin layer of 
white matter. 

In the posterior quadrige»iinal bodies the white fibers are con- 
tinuous, behind, with the lower fillet; and with the posterior bra- 
chium, antero-externally. Their whole interior is gray matter. 
In it are a network of fine fibers, and small multipolar cells. 
The latter are probably the terminals of the lower fillet fibers. 
The posterior bodies are united beneath the sulcus longitudinalis 
both by decussating fibers of the fillet and by gray matter. In 
distinction from the anterior bodies, the posterior pair may be 
called the auditory lobes; they are well marked only in those 
mammals having highly specialized organs of hearing. 

The anterior pair of the corpora quadrige7nina represent the 
corpora bigemina, the optic lobes, of birds, fishes and reptiles. 
They are composed of three laminas: (1) The superficial white 
matter, the stratum zvnale. This and the fibers of their interior, 
are continuous, through the anterior brachium, with the optic 
tract. Many of them are crossed fibers. (2) The stratum cin- 
ereum forms a cap of gray matter beneath the stratum zonale. In 
structure it resembles the interior of the posterior bodies. (3) Its 
multipolar cells increase in size toward the second gray layer, the 
stratum opticum. In that, the cells are very large. They are 
grouped in masses between the abundant fibers from the outer 
root of the optic tract. The stratum opticum rests upon the 
quadrigeminal lamina. Some gray matter is scattered through 
the latter, and Tartuferi calls it the "stratum lemnisci." 

The internal geniculate bodies form a part of the tegmentum. 
They arise from the mesencephalon with the remainder of the 
mid-brain to which they belong; but for convenience, they were 
considered with the external geniculate bodies under the heading 
'inter-brain," (which see). 

THE GRAY AND WHITE MATTER OF THE CEREBRUM AND 
MID-BRAIN. 

In the Mid-brain, white matter is found in the crustae and teg- 
mentum, separated by the gray substantia nigra, and on its doisum 
are the corpora quadrigemina and internal geniculate bodies, 
composed of gray matter. Gray matter forms nearly the whole 
of the inter-brain. The greater part of the hemispheres is white 



44 The Brain and Spinal Cord. 

matter ; only a thin envelope of gray matter, the cortex, incloses 
it. Imbedded in that white matter, is the basal ganglion of the 
hemisphere, called the corpus striatum. Both the gray and the 
white matter are richly supplied with blood vessels. 

The white matter is composed of medullated nerve fibers of 
various sizes arranged in bundles and separated by neuroglia. 
The fibers are without a neurolemma in the whole cerebro-spinal 
axis. They are the medullated axis-cylinders, or axons, of cells in 
the gray matter. 

The gray matter contains two nerve elements — nerve cells 
and nerve fibers, which are embedded in an abundance of neurog- 
lia. The cells are of various shapes, such as spherical, fusiform, 
pyramidal and polymorphous; and they possess from one to eight 
or a dozen processes. They are nucleated cells. In diameter 
they range from 10 micromes to 50 micromes. The cell processes 
a.:e of two kinds, viz., the dendrites, or afferent processes (the 
protoplasmic); and the axons, axis-cylinder or efferent processes. 
The dendrites and a few axons ramify in the gray matter, forming 
its fibers. For the most part, fibers in the gray substance are non- 
medullated. The greater number of axons, receiving the white 
substance of Schwann, pass down into the white matter. 

Two forms of sustentacular tissue are found in the brain and 
Spinal cord: (1) Neuroglia, which is most abundart in gray 
matter, is an epiblastic structure made up of richly branched 
nucleated cells whose processes form a fine reticulation in the 
larger meshes of the connective tissue network. (2) The con= 
nective tissue network. It is of mesoblastic origin and is formed 
by branching processes from the inner surface of the pia mater. 
It transmits the blood vessels into the nervous substance. 

THE NEURON— (WALDEYER), 

Recent investigations appear to prove that the nervous system 
is composed of myriads of independent neurons, imbedded in 
neuroglia and supported by a connective tissue frame-work. The 
neuron is an individual, nervous entity, structurally independent 
of every other neuron. But by association, or proximity, every 
neuron is intimately related to other neurons. 

The neuron is made up o£ a nerve cell, and its processes. The 
cell forms the center of the neuron. The cell may be situated in 
the brain, the spinal cord or a ganglion. The processes are of 
two varieties: 1. The dendrites (His), or the protoplasmic, affer- 
ent or sensory processes. 11. The axon (Kolliker), or the axis- 



Ckrebrum and Mid-Brain. 45 

cylinder, efferent ox motor process. Each neuron usually possesses 
a number of dendritic processes. One axon to a cell is most com- 
mon, but there are, also, diaxons, triaxons and polyaxons. 

I. Dendrites— their characteristics. 

1. Are a part of the cell and protoplasmic in composition. 

2. May be absent, or very numerous. 

3. Are knotted (gemmulated) and richly branched. 

4. May be short (as in brain and spinal cord) and ramify 
in adjacent gray matter. 

5. May be long (as in spinal ganglia) and terminate in 
distant part, as the skin. 

6. They end free, and either pointed, or bulbous as in 
special end organs. 

7. They are medullated or non-medullated. 

8. They end independently and either at the periphery 

or, in thebrain and cord, in relation with the end tufts 
of other neurons. 

9. Functions are afferent: (1) Trophic, carry nutrition to 
cell and axon; (2) Sensory, carry impulse to the cell. 

II. Axons, their characteristics: — 

1. They are especially differentiated parts of the cell and 
are fibrillar. 

2. Are smooth; and, except in the cerebellum, are of con- 
siderable length. Many reach from the brain to the 
spinal cord, or vice versa, or from the cord to the mus- 
cles of the extremities. 

3. They branch freely at the end, forming end-tufts, end- 
brushes, or filamentous ramifications, which are in rela- 
tion with a muscle or with other neurons. They always 
end structurally free. 

4. They give off collateral branches (paraxons) which are 
in every respect similar to the main axon. 

5. They are medullated, 

6. Functions are efferent. (1) Trophic, carry nutrition to 
muscle; and (2) Motor, carry impulse to muscle. 

7. On section, the part cut off dies; but the part joined to 
cell and the cell itself do not. 

ORDER OF NEURONS. 

i st Order. — End-tufts are connected with the periphery. 
2d Order. — End-tufts are in relation with former neuron. 

GOLGl'S TYPES OF CELLS. 

1st type have long axon, forming distinct fiber, as in a nerve 
(inaxon). In brain and spinal cord. 

2d type have short axon, which breaks up into branches at 
once (dendraxon). In cerebellum. 

Axodendron — A fibrillar dendrite (Golgi) given off at the ori- 
gin of the axon. It is afferent in function. 



46 The Brain and Spinal Cord. 

The gray matter of the cerebrum and mid-brain is conven- 
iently grouped into three classes: 
I. Cortical. 
II. Ganglionar. 
III. Central or Ventricular. 

(This classification disregards the scattered gray matter of the 
tegmentum). 

I. THE CORTICAL GRAY MATTER. 

It consists of a thin envelope, the cortex (or bark), which forms 
the surface of the hemispheres and incloses the (white) medulla. 
The cortex varies in thickness from a line to a quarter of an inch. 
Thickest on the surface of the convolution, it grows thinner to the 
bottom of the sulci. It is of a reddish, or yellowish, gray color 
depending on the richness of the blood supply. To the naked eye, 
a fresh specimen shows a stratified arrangement: sometimes three 
gray laminae can be made out which are sepaiated by the in^er 
and outer white lines of Bailarger; and, in the hippocampal gyrus, 
a superficial (reticulated) white layer also is easily seen. A typ- 
ical section of cortex, which is usually taken from the parietal 
lobe, presents under the microscope five layers, as follows: 

(i) The superficial, molecular, or neurogliar layer — It is 
next the pia mater. Neuroglia forms the bulk of it, but it con- 
tains a few irregular nerve cells, possessing dendritic and from 
one to three axonic processes; and a fine network composed of 
gray and medullated nerve fibers. These medullated fibers form 
the superficial white layer, above referred to, visible to the naked 
eye in the gyrus hippocampi. The fibers in the neurogliar layer 
are for the most part dendrites of cells in subjacent laminae. 

(2) The second layer is the layer of small pyramidal cells. 
The pyramids are closely packed together. They point toward 
the pia. Their dendrites run outward and ramify in the neurog- 
liar layer; their bases, from which the axons issue, are directed 
toward the white core of the convolution. The axons, after pierc- 
ing the deeper gray laminae, receive the white substance of 
Schwann and enter into the formation of the medulla of the 
hemisphere. 

(3) Third, the layer of large pyramidal cells— The large 
pyramids have the same direction as the small ones. They are 
arranged in elongated groups separated by radiating fibers. The 



Cerebrum and Mid-Brain. 47 

pyramids are largest and the grouping most distinct near the 
fourth layer. Their dendritic processes pass outward; their 
axons, as medullated fibers, run down into the white center. 
Seven or eight collaterals are given off from each axis-cylinder 
process before it becomes medullated, and these collaterals ramify 
in the adjacent gray matter. 

The third layer is as thick as the two overlying it; it varies 
between 1-50 of an inch and 1-25 of an inch. Its formation is like 
that of the cornu Ammonis (the hippocampus major.) 

(4) Fourth, the polymorphous celled layer is a very thin 
one, about 1-100 of an inch in thickness. Its cells are small and 
irregular. They possess many dendrites and one axon, or axis- 
cylinder process. A few of the latter, piercing the third and sec- 
ond layers of gray substance, ramify in the first: the larger num- 
ber of them pursue the usual course into the white center. The 
latter become projection fibers. 

(5) Fifth— This is the layer of fusiform cells. It has the 
formation of the claustrum, hence the synonym, claustral forma- 
tion. It is placed next the white center. It is a thick layer (1-25 
inch), and merges imperceptibly into the medulla beneath it. The 
fusiform cells, in the main, have their long axes perpendicular to 
the surface of the hemisphere; but, beneath the fissures, they are 
parallel with it. In the convolutions they lie between the radiat- 
ing fibers. Under the sulci, they are parallel with the association 
fibers which join adjacent gyri. 

To this typical cortex there are four principal exceptions, viz.: 

(a) On the mesial surface of the occipital lobe near the calca- 
rine fissure, there are six to eight layers produced by the division 
of the layer of large pyramids by a lamina of irregular cells with 
or without the presence of the normal fourth layer. The latter 
may divide the layer of fusiform cells. There are very few large 
pyramids in this situation. The pyramidal cells are largest in 
the Rolandic area. 

(b) The gray cap of the olfactory bulb has but four layers, 
namely: First, the nerve fiber layer composed of the non-medul- 
lated fibers of the olfactory nerves which join the bulb from below; 
second, the stratum glomerulosum, the glomeruli being made up 
of the olfactory fibers and of the dendrites of the mitral cells; 
third, the layer of mitral cells, whose protoplasmic processes 
ramify in the second layer and whose axons pass into the medul- 



48 The Brain and Spinal Cord. 

lary stem, after piercing the granular layer; and fourth, the gran- 
ular layer, which lies next the medullary stem and is composed 
of small irregular cells like those in the rust-colored granular 
layer of the cerebellum. The last two (the third and fourth) are 
sometimes called the granular layer, thus reducing the number 
to three. The axis-cylinder processes of the mitral (or conical) 
cells, medullated, form the olfactory tract. 

(c) In the hippocampus major are four layers of cortical 
matter. The first layer, the one bounding the dentate fissure, is 
the involuted medullary lamina. This is the regular network of 
medullated fibers, but is more highly developed than in typical 
cortex. It is just beneath the pia, a little neuroglia only inter- 
vening. The second layer is composed of closely packed small 
cells. It is the stratu?7i granulositm. There are no cells in the 
third layer, but a dense network of pyramidal dendrites. The 
fourth is a very thick layer and is made up of pyramidal cells of 

medium size. Their medullated axons constitute the thin lamina 
of white matter called the alveus which forms the ventricular sur- 
face of the hippocampus major. 

(d) The fourth exception to the typical cortex is found in the 
floor of the fissure of Sylvius. It consists of a very great 
thickening of the fusiform layer. All five laminae are present. 
This cortex resembles the claustrum. 

The claustrum (a rampart) is an isolated sheet of gray 
matter in structure much like the fifth layer of the cortex. It is 
cortical matter according to Meynert. It is a vertical antero- 
posterior sheet placed mesial to the island of Reil, and lateral to 
the external capsule. The surface in contact with the external 
capsule is smooth, but the external surface is convoluted to 
coincide with the gyri insulae. At its lower border it joins the 
lenticular nucleus. It is made up of fusiform cells which lie 
between the fibers of the uncinate fasciculus (See below — associa- 
tion fibers). 

II. GANGLIONAR GRAY MATTER. 

It is found in the great ganglia which have already been con- 
sidered. They should be re-studied in this connection. They 
are as follows: 



Cerebrum and Mid-Brain. 49 

(1) In the hemisphere: 

Corpus striatum, composed of the caudate and lenti- 
cular nucleus. 

(2) In the inter-brain: 

The optic thalamus, and the external geniculate 
body. 

(3) In the mid-brain: 

The internal geniculate body, the anterior and the 
posterior quadrigeminal body, and a lateral half of 
the substantia nigra. 

III. CENTRAL, OR VENTRICULAR GRAY MATTER. 

It is located (1) in the floor and walls of the third ventricle, (2) 
in the middle commissure of that ventricle, and (3) around the 
Sylvian aqueduct. 

(1) The lamina cinerea and tuber cinereum form a sheet of 
gray substance that connects the interior surfaces of the hemi- 
spheres and may be called their inferior (or screat) gray commissure. 
From the floor of the third ventricle it extends laterally beneath 
the optic thalamus, and is continuous with the anterior perforated 
lamina. The gray matter of the floor extends up a short distance 
on the mesial surface of the thalamus opticus; and in that up- 
turned part is located the anterior end of the motor-oculi nucleus. 
(2) The middle commissure joins the internal nuclei of the op- 
tic thalami; and is, also, continuous with this upward extension of 
the gray floor. In the middle commissure are nerve-cells and 
transverse fibers. The latter appear to be loops which reach only 
to the median line; at least many of the fibers do not cross to the 
opposite side. (3) The nucleus of the third and that of the fourth 
cranial nerves are found ih the gray matter about the Sylvian 
aqueduct. In it, also, is a part of the motor nucleus of the trigemi- 
nal or fifth nerve. 

The white matter of the cerebrum and mid-brain is com- 
posed of three definite systems of fibers: 

i. Projection, or peduncular, fibers. 

2. Transverse, or commissural, fibers. 

3. Association fibers. 

1. PROJECTION FIBERS. 

They are the medullated axis-cylinders of the large and me- 
dium-sized pyramids, and of a few of the polymorphous cells in the 



50 The Brain and Spinal Cord. 

cortex. The projection fibers include those which run through 
the mid-brain to the cerebral cortex or vice versa, and those ra- 
diating to the cortex which originate in the striate body or the op- 
tic thalamus. The greater number pass through (form) the in- 
ternal capsule, and then diverge in all directions in the corona 
radiata. 

Fibers from the crusta of the mid-brain make up the superior 
lamina of the internal capsule and end in the prefontal, the Ro- 
landic and the parietooccipital cortex. 

The tegmental fibers first enter the optic thalamus or the cor- 
pus striatum. After which they probably proceed, chiefly 
through the internal capsule, to almost every part of the cerebral 
cortex. In the inner capsule the projection fibers give off collat- 
eral branches, some of which end in the ganglia above mentioned 
and others pass through the corpus callosum to the cortex of the 
opposite hemisphere. (See crusta and tegmentum under mid- 
brain). 

II. commissural fibers. 

They connect opposite sides of the cerebrum. They are con- 
tained in the corpus callosum and the anterior commissure, per- 
haps a few fibers in the posterior commissure. 

The corpus callosum is the great link between tfce hemi- 
spheres. Its fibers connect both similar and dissimilar parts of the 
cortices. It is made up of cortical axons, a few of them being 
projection fibers; and collaterals from the projection fibers. All 
callosal fibers except the few peduncular fibers, end on the oppo- 
site side in arborizations about the cortical cells. 

The anterior commissure joins the temporal lobes together 
(pars temporalis); and the temporal lobe with the contra-lateral 
olfactory tract (pars olfactoria). 

in. association fibers. 

These fibers remain on the same side and connect parts of the 
same hemisphere. They are situated close to the cortex, the 
various parts of which they serve to unite. The short association 
fibers join adjacent convolutions. They are the more numerous. 
The long association fibers are collected into bundles. Among 
the best marked are the following: 

(i) The fillet of the gyrus fornicatus is a bundle of fibers in 
the falciform gyrus (the fornicate and hippocampal gyri) which 
almost entirely encircles the corpus callosum. It extends from 



Cerebrum and Mid-Braix. 51 

the anterior perforated lamina, through the gyrus fornicatus and 
hippocampal convolution, to the uncus. The fibers have a 
tendency to radiate toward the cortex on the convex surface. 

(2) The fornix — Each lateral half of the fornix is a bundle of 
association fibers. Its anterior end (or pillar) is connected with 
the corpus albicans; and, through the bundle of Vicq d'Azyr, also 
with the optic thalamus. The posterior pillar, descending in the 
middle horn of the lateral ventricle, for the most part, disappears 
in the alveus of the hippocampus major; but a small bundle of its 
fibers, constituting the corpus fimbriatum, continues to the uncus. 

(3) The uncinate funiculus is a bundle, with some sharply 
curved fibers, which arches over the main stem of the Sylvian 
fissure, and connects the frontal and temporal lobes. It is situ- 
ated near the basal surface. Its fibers spread out at both ends in 
the cortex, and they especially join the third frontal convolution 
with the temporal and limbic lobes (Schafer). 

(4) The superior longitudinal funiculus is a sagittal bundle 
located beneath the convex surface of the hemisphere. It joins 
the frontal cortex with the parietal and the external temporal. 

(5) The inferior longitudinal bundle is about on a level with 
the lateral ventricle. It passes near the outer wall of the 
descending and posterior cornua of that ventricle. It connects 
the temporal lobe to the occipital. In the temporal lobe its fibers 
cross at right angles those of the inferior lamina of the internal 
capsule. 

(6) The perpendicular funiculus— This is a vertical bundle 
located just in front of the occipital lobe. It extends from the 
inferior parietal convolution, above, down to the fourth temporal, 
or fusiform, gyrus. 

SOME ESSENTIAL FACTS OF DEVELOPMENT. 

A glance at the origin of the principal parts of the cerebrum 
and mid-brain will assist us at this time. 

The brain and spinal cord are developed from the neural 
tube. That tube is of epiblastic origin, and is the successor of 
the neural groove, which by elevation and closing in of its borders 
is converted into a tube. By the fifteenth day after conception 
the tube is closed, except at its posterior extremity. The cephalic 
(closed) end of the tube is much larger than the caudal end; and 
presents at the fifteenth day two constrictions that separate the 



52 The Brain and Spinal Cord. 

primary brain vesicles from one another— the anterior, the 
middle and the posterior. 

Behind the posterior primary vesicle, the neural tube remains 
small and of nearly uniform size; it forms the spinal cord* 

The brain vesicles grow rapidly. By the end of the fourth 
week a constriction is visible in the anterior primary vesicle and 
another in the posterior vesicle, dividing each into two and mak- 
ing in all five secondary brain vesicles, which freely communi- 
cate with one another and are numbered from before backward. 
They are: — 

i. Prosencephalon. 

2. Thalamencephalon. 

3. Mesencephalon. 

4. Epencephalon. 

5. Metencephalon. 

These vesicles form the brain, their cavities become the 
ventricles. Two kinds of cells appear in the vesicle walls; the 
neuroblasts and spongioblasts. The neuroblasts produce the 
nerve cells and fibers. The supporting neuroglia is formed from 
spongioblasts. 

Flexures— The cephalic portion of the neural tube is the seat of 

three flexures, two ventral and one dorsal. (1) The mesencephalic 
flexure (ventral) begins very early and amounts to 180 degrees by 
the 28th day. It bends ventrally the thalamencephalon until it al- 
most touches the epencephalon. (2) The cervical flexure is also 
a ventral one. It is located at the junction of the fifth vesicle with 
the spinal cord, and corresponds to the bending of the head upon 
the body of the embryo. This flexion begins about the 21st day. 
By the end of the fourth week, it is completed and amounts to 90 
degrees. (3) The dorsal flexure is beginning to form at the same 
time (4th week). It occurs between the fourth and fifth brain ves- 
icles,, and is often called the metencephalic flexure. It reaches 
180 degrees by the eighth week, when the dorsal part of the epen- 
cephalon (the cerebellum) rests upon the metencephalon (the 
medulla oblongata). 

Meninges— The neural tube is surrounded by mesoblast which : 
in course of development, forms the pia mater, the arachnoid and 
the dura mater. 



Cerebrum and Mid-Brain. 



53 



Brain Vesicles and Their Derivatives. 



Primary V. Secondary V. 



Anterior 

( Fore-brain) < 



ist. The Prosen= 
cephalon. 



2d. The Thala- 
mencephalon. 



Middle 

(Mid-brain) 



( 3d. The Mesen 
( cephalon. 



Derivatives. 

Hemispheres, and Ante= 
rior wall of 3d Ventricle. 

(Foramina of Monro, lat- 
eral ventricles, hemi- 
spheres, corpora striata, ol- 
factory lobes, fornix, an- 
terior commissure, corpus 
callosum, choroid plexus 
of lateral veutricle, and 
lamina terminalis.) 

Inter=brain and Third 
Ventricle, except anterior 
wall. (Optic thalami, ex- 
ternal geniculate bodies, 
posterior and middle com- 
missures, pineal body, 
choroid plexuses of 3d 
ventricle and the 3d ven- 
tricle, corpora albicantia, 
tuber cinereum and in- 
fundibulum, lamina cin- 
erea, retinae, optic nerves, 
^chiasma and tracts.) 



f Mid-brain and Aqueduct 

I of Sylvius. (Crustae, sub- 
: I stantia nigra, tegmentum, 
] Sylvian aqueduct, corpora 
I quadrigemina and internal 
^geniculate bodies.) 



Posterior 

(Hind-brain) 1 



4 th. The Epen-( Hind - b, ? ln 'TO 

„„i, a i A . •) pons and cerebel- 

cephalon. J f um } 4th 

|>Ven= 



5th 



I 



The Meten- ( A " er r brai "' The ! tride - 

cephlaon. 1 medulla oblonga- 



ta.) 



J 



The cerebrum is developed from the anterior primary brain 
vesicle as is shown in the outline, being the more immediate 
descendant of the prosencephalon and thalamencephalon. 

PROSENCEPHALON. 

It is at first a single vesicle forming the fore part of the anterior 



54 The Brain and Spinal Cord. 

primary vesicle. The mesial portion of its anterior wall (lamina 
terminalis) remains almost stationary ,but, laterally, it is the seat of 
rapid growth and produces on either side a hollow diverticulum, 
whose cavity is the primitive lateral ventricle and whose walls 
form the substance of the hemisphere. The outgrowth is called 
the hemisphere vesicle, its constricted stalk contains the primi- 
tive foramen of Monro. The vesicles grow forward at first, 
separated from one another by mesoblast which forms the falx. 
Later, growth occurs in succession, upward, backward, and down- 
ward, until by the seventh month the hemisphere overhangs every 
other part of the brain. 

Sulci — The vesicle walls are of uniform thinness up to the 
second month,and during their rapid growth in the second and third 
months, become thrown into folds which encroach upon the cavity 
and present on the surface of the vesicle (or hemisphere) the 
primary sulci. The cause of the infoldings is, perhaps, the re- 
sistance of the slower growing cranium. The primary sulci are 
best developed in the third month. Their location nearly corre- 
sponds to the following permanent fissures: Sylvian, Parieto- 
occipital, Calcarine, Hippocampal, Collateral and (anterior exten- 
sion of) Great Transverse fissure. For the most part the primary 
sulci have disippeared by the first of the fifth month (at this stage 
the cranium grows more rapidly than the brain vesicles), but the 
ventricular eminences produced by the sulci remain permanently, 
namely, the hippocampus major and ?ninor, eminentla collateralis 
and possibly the caudate nucleus. 

In the sixth month the primary sulci are replaced by the im- 
portant permanent fissures, which divide the hemisphere into 
lobes. Many of the smaller permanent sulci appear after birth. 
The permanent fissures and sulci are the result of depressions in 
the surface;they do not involve the whole thickness of the ventric- 
ular wall. Their object is probably to preserve a certain ratio 
between the cortex and the white matter in the hemisphere. (For 
the permanent fissures see surface of cerebrum). Two of the per- 
manent fissures are peculiar, viz: 

(i). The fissure of Sylvius, which is formed by the approxima- 
tion of the anterior and posterior walls of the broad Sylvian val- 
ley ox primary sulcus in the ventral border of the hemisphere. 
The bottom of the valley develops the corpus striatum and the 
island of Reil. The latter is concealed before birth by a back- 



Cerebrum and Mid-Brain. 55 

ward and downward growth of the anterior wall, the operculum. 
The forward and downward growth of the posterior wall com- 
pletes the fissure and forms the temporal lobe. 

(2). The anterior extension of the great transverse fissure. 

— It is produced by a curved invagination of the mesial wall of 
the hemisphere vesicle. Beginning just behind the stalk of the 
vesicle (containing the foramen of Monro), it extends back to the 
posterior end of the optic thalamus (in the adult) and then bends 
downward and forward toward the apex of the temporal lobe. It 
involves the entire thickness of the vesicle wall, though it is a 
permanent fissure, and the fold which it pushes into the lateral 
ventricle persists as a single layer of epithelium investing the 
choroid plexus. 

Olfactory lobe — In the fifth week a hollow diverticulum grows 
out from the antero-iiferior wall of the hemisphere vesicle, and 
forms a prominent lobe. It preserves a lobular form in the horse, 
and in some other animals; but in man it soon becomes con- 
stricted by the fissura prima into anterior and posterior lobule, 
and loses its ventricular cavity. The anterior olfactory lobule 
develops; the bulb, tract, trigone, and area of Broca ; the poste= 
rior lobule forms the anterior perforated lamina. 

Thickenings — The walls of the hemisphere vesicle thicken 
rapidly, as the vehicle grows in size, and form the cortical and 
medullary substance. By the end of the second month the corpus 
striatum is well formed, near the middle of the floor of the hemi- 
sphere; and a ridge appears about the same time in the mesial 
wall of the vesicle, just above the forward extension of the great 
transverse fissure. That ridge develops into a bundle of fibers, 
constituting a lateral half of the fornix. 

Fusions— The hemisphere vesicle so increases in size by the 
eighth week of embryonic life as to come in contact with its fel- 
low of the opposite side, and with the dorsal and lateral surface of 
the thalamencephalon. At those two points of contact certain fu- 
sions occur: 

(1) The hemisphere vesicles touch one another in front of the 
lamana terminalis. The area of contact is at first small and is 
crescentic in shape, the convexity of the crescent looking forward 
and its horns diverging backward like a "wet moon." Along the 
borders of this crescent the two hemisphere grow together. The 
crescents themselves remaining free, form the septum lucidum 



56 The Brain and Spinal Cord. 

and inclose between them the fifth ventricle. A strong round bun- 
dle of fibers is thrown across at the inferior angle of the crescent, 
which is the anterior commissure. Pressure of the anterior com- 
missure against the lamina terminalis causes the latter to be ab- 
sorbed back to its lining epithelium. That epithelium separates 
the commissure from the 3d ventricle in the adult. Fusion occurs 
next along the concave border (the postero-inferior) of the cres- 
cent. That border coincides with the fornix "ridge" above re- 
ferred to; and fusion of the two ridges forms the body of the for- 
nix. The anterior pillar hooks around the foramen of Monro, 
and turns back into the lateral wall of the thalamencephalon; the 
posterior pillar grows backward with the hemisphere. Last, fu- 
sion occurs along the convexity of the crescent. It forms the cor- 
pus calloswn. The rostrum and genu are first developed. Like 
the fornix, it grows with the hemispheres backward until com- 
pleted. 

(2) Fusion occurs between the hemisphere vesicle and the lat- 
eral surface and a small part of the superior surface of the thal- 
amencephalon. The blending of the mesial wall of the hemi- 
sphere and the external surface of the thalamencephalon forms 
that fan-shaped group of fibers called the superior lamina of the 
internal capsule. On the superior surface of the thalamencepha- 
ilon, fusion takes place as far mesially as the oblique groove on the 
optic thalamus (which see). Here the hemisphere wall is repre- 
sented by a single layer of epithelium, which invests the optic 
thalamus, superiorly, external to the "groove." It is continuous 
toward the median line with the fold inclosing the choroid plexus; 
and it extends between the taenia semicircularis and margin of the 
fornix. The epithelium is in continuity with the ependymal lin- 
ing of the lateral ventricle. 

Velum interpositum— The growth of the meninges and brain 
vesicles occurs pari passu. The pia mater is at all times in con- 
tact with the surface of the vesicles; and it gives off branching 
trabecules, which form the connective tissue network of the nerve 
substance. Wherever fusion between the brain vesicles occurs, 
the two layers of pia are absorbed: and 'they unite with one 
another just beyond the line of fusion. Thus they unite above 
the corpus callosum and beneath the fornix, when those connect- 
ing links are formed between the hemispheres. The pia beneath 
the fornix is, therefore, continuous with that covering the lower 



Cerebrum and Mid-Brain. 57 

half of the mesial wall of each hemisphere; and, by growth of the 
hemispheres and fornix, it is carried back over the pia investing 
the thalamencephalon. Fusion of the latter with each hemisphere 
causes absorption of the double layer of pia mater upward to the 
thalmic "groove," and union of the two laminae along that 
"groove." The result is a triangular sheet made up of two layers 
of pia, the velum interposition. It separates the fornix from the 
inter-brain in the mature organ. Its borders form the choroid 
plexus of each lateral ventricle; they converge forward to the 
foramen of Monro. 

THALAMENCEPHALON. 

This is the posterior division of the anterior primary vesicle. 
It forms the inter-brain, and the third ventricle \ except its an- 
terior boundary. Before it is constricted off from the prosen- 
cephalon, the optic vesicle makes its appearance on either side. It 
is a prominent diverticulum at first; but it grows, in man, less rap- 
idly than the vesicle from which it arises. The optic vesicle be- 
comes cupped and is the primitive retina. From it the optic 
nerves grow back to the ventral surface of the thalamencephalon, 
where the optic chiasma and tracts are developed. Later, the 
tracts grow back along the side of the thalamencephalon, and be- 
come connected with the corpora quadngemina. 

The optic thalamus is formed by thickening of the lateral 
wall of the second vesicle. It fuses externally with the hemi- 
sphere (corpus striatum) and forms the superior lamina of the 
internal capsule. Internally, it fuses with its fellow of the oppo- 
site side, forming the middle commissure. 

From the floor of the thalamencephalon are developed the 
corpora albicantia (at first single); the tuber cinereum and infun- 
dibulum; the lamina cinerea and optic commissure. 

The superior wall or roof of this second vesicle stretches out 
and becomes very thin, except at its posterior extremity where it 
develops a transverse white band, the posterior commissure. Im- 
mediately in front of this commissure, a diverticulum of the roof 
appears which is the primitive pineal body. Two longitudinal 
folds of the roof dip down into the ventricular cavity. These are 
followed by two like downward projecting folds from the inferior 
lamina of the velum interpositum, which constitute the choroid 
plexuses of the third ventricle. 



58 The Brain and Spinal Cord. 

MESENCEPHALON. 

This is the embryonic mid-brain. It is the third of the second- 
ary vesicles. The elbow of the mesencephalic flexure of 180 de- 
grees is formed by it; and that flexure almost brings the thala- 
mencephalon and epencephalon in contact with one another be- 
neath it. The mesencephalon remains small, but its walls thicken 
greatly. As a result of the thickening, its cavity is reduced to a 
slender canal, the aqueduct of Sylvius. The walls form, ven- 
trally, the crustae, substantia nigra and part of the tegmentum, 
and dorsally, the remainder of the tegmentum. About the third 
month the dorsaMhickening is divided in two by a fore and aft 
groove, the sulcus longiiudinalis. A transverse groove appears 
two months later and completes the outline of the corpora quad- 
7'igemina. 

The epencephalon develops the pons and cerebellum; the 
metencephalon, the medulla oblongata; and their common cav- 
ity is the fourth ventricle. 

BLOOD SUPPLY OF THE CEREBRUM AND MID-BRAIN. 

The blood supply of the cerebrum and mid-brain is derived 
from the anterior choroid and the anterior and middle cerebral 
arteries, all branches of the internal carotid; and from the poste- 
rior cerebral arteries, which are the terminal branches of the bas- 
ilar artery. They form a remarkable anastamosis at the base of 
the brain, the circle of Willis. The circle of Willis (really a hep- 
tagon) extends from a point in the great longitudinal fissure, an- 
terior to the optic commissure, back to the pons. It is about an 
inch and a half long, and one inch in transverse diameter. In 
front are the anterior cerebral arteries converging forward from 
the internal carotids, and uniting through the anterior communi- 
cating artery. The posterior communicating artery forms the 
lateral boundary of the circle. It forms the anastamosis between 
the internal carotid artery and the posterior cerebral. The pos- 
terior cerebral arteries bound the circle behind. 

CORTICAL SYSTEM. 

The large distal branches of the cerebral arteries are distribu- 
ted chiefly to the hemispheres; while the small proximal branches 
supply the ganglia and inter-brain. The former belong to the 
cortical system, the latter to the ganglionic system. 



Cerebrum and Mid-Brain. 59 

The anterior cerebral artery enters the great longitudinal fis- 
sure. Winding around the genu of the corpus callosum, it runs 
back on the mesial surface of the hemisphere to the parieto-oc- 
cipital fissure. It has three branches: (1) Anterior internal 
frontal, which supplies the internal orbital convolution and ol- 
factory bulb, the superior frontal and the anterior half of the mid- 
dle frontal gyri. (2) Middle internal frontal, distributed to the 
corpus callosum, gyrus fornicatus, marginal convolution and up- 
per end of the ascending frontal convolution. And, (3) Poste- 
terior internal frontal, to the quadrate lobe. 

The middle cerebral artery runs in the fissure of Sylvius. It 
has four distal branches: (1) External and inferior frontal, to the 
third frontal convolution; (2) Ascending frontal, and, (3) Ascend- 
ing parietal to convolutions of the same name, and, (4) parieto- 
temporal, which supplies the angular and superior temporal gyri. 

The posterior cerebral artery, winding from the basilar artery 
outward around the mid-brain, breaks up into three cortical 
branches on the tentorial surface of the hemisphere. Their dis- 
tribution is as follows: (1) Cuneate, to the cuneus and the convex 
surface of the occipital lobe; (2) Uncinate, to the same convolu- 
tion, and, (3) Temporal, (or tempero-sphenoidal) to the fourth, 
third and part of the second temporal gyri. 

These vessels of the cortical system pierce the hemispheres 
perpendicular to the surface. They are distributed (the short) to 
the cortex and (the long) to the medulla of the hemispheres. To a 
limited extent they anastamose with one another, but they do not 
communicate with the ganglionic system. 

GANGLIONIC SYSTEM. 

Small arteries from the circle of Willis and from the cerebral 
arteries near the circle constitute this system. It is made up of six 
groups of vessels: 

(1) Anteromedian ganglionic— They arise from the anterior 
cerebral arteries and anterior communicating. Piercing the lam- 
ina cintrea (and a few of them, the anterior perforated lamina) 
they supply the bulb of the caudate nucleus and anterior wall of 
the third ventricle. 

(2) and (3). The anterolateral ganglionic arteries take their 
origin, on either side, from the middle cerebral artery, a little out- 
side the circle of Willis. They pierce the anterior Derforated 



60 The Brain and Spinal Cord. 

lamina; and are distributed to the striate body, internal capsule 
and optic thalamus. One of this group is the lenticulo-striate 
artery. It supplies almost the entire corpus striatum. On ac- 
count of its frequent rupture, it is called the artery of cerebral 
hemorrhage. (Charcot). 

(4) Postero=median ganglionic— These are branches of the 
posterior ce ebrai and posterior communicating arteries. They 
supply the interpeduncular structures and crustae; and (after 
piercing the posterior perforated lamina) the walls of the third 
ventricle and mesial parts of the optic thalami. 

(5) and (6) Postero= lateral ganglionic arteries — They arise, 
on either side, from the posterior cerebral artery, after it has 
wound around the crusta. They are distributed to the posterior 
part of the optic thalamus, the geniculate bodies and corpora 
quadrigemina. 

The ganglionic arteries pass to their distribution without com- 
municating with one another or with the cortical arteries. They 
are the end=arteries of Cohnheim. Between the cortical and 
ganglionic systems, there is an area poorly supplied with blood. 
That is the area of cerebral softening. 

Choroid arteries— They are three in number: 

Anterior choroid— Coming from the internal carotid artery, it 
enters the apex of the descending horn of the lateral venticle; and 
supplies the inferior two-thirds of the choroid plexus, a part of the 
velum interpositum, the hippocampus major and corpus fimbri- 
atum. 

The postero-lateral choroid is a branch of the pos f erior cere- 
bral. It is distributed to the upper third of the choroid plexus of 
the lateral ventricle and to the velum interpositum. 

Postero-mesial choroid — Also a branch of the posterior cere- 
bral artery, it supplies the choroid plexuses of the 3d ventricle; 
and, with branches from the superior cerebellar, completes 
the supply of the velum interpositum. The postero-lateral and 
postero-mesial choroid vessels have their origin, course and dis- 
tribution wholly within the great transverse fissure. 

Veins— The velum interpositum and lateral and 3d ventricles 
are drained by the veins of Galen. The veins of Galen are formed, 
on either side, at the foramen of Monro by the union of the veins 
of the striate body and choroid vein. 

The superior cerebral veins, eight to twelve in number, carry 



Cerebrum and Mid-Brain. 6i 

away the blood from the superior surface of the hemisphere. They 
ran obliquely upward and forward 'into the superior longitudinal 
sinus. Just before emptying into the sinus they receive most of 
the median veins. 

The median cerebral veins— They drain the mesial surface of 
the hemisphere. The veins of the mesial surface which do not 
empty into the superior cerebral veins unite and form the inferior 
longitudinal sinus. 

The base of the cerebrum and border of its convex surface are 
drained by the inferior cerebral veins. On the tentorial surface of 
the hemisphere, these veins empty, against the current, into the 
lateral and superior petrosal sinuses. Those from the temporal 
and frontal lobes, empty into the cavernous sinus. In or near 
the fissure of Sylvius there are two inferior cerebral veins of large 
size. The middle cerebral vein, which runs from the under sur- 
face of the temporal lobe, mesially, along the fissure of Sylvius 
to the cavernous sinus; and the great anastamotic vein of Trolard, 
whose course is much the same but in front of the Sylvian fissure. 
Arising on the parietal lobe, it winds inward along the lesser 
wing of the sphenoid bone to the anterior extremity of the cav- 
ernous sinus. 



HIND-BRAIN. 



THE CEREBELLUM. 

The hind-brain is composed of the cerebellum and the pons. 
The cerebellum is the dorsal portion of the hind-brain. It is 
called the little brain. Its weight is about 5 oz., slightly more 
than one-tenth of the whole brain. It is situated in the posterior 
fossa of the skull, under the tentorium cerebelli and dorsal to the 
pons and medulla oblongata. Between it and the last two struct- 
ures is inclosed the fourth ventricle. The cerebellum is made up 
of two lateral parts, the hemispheres, and a central part, uniting 
the hemispheres together, called the worm. 

The cerebellar hemispheres measure two inches from before 
backward and about the same in thickness, antero-internally; but 
they taper rapidly toward the lateral borders. They are joined 
together by the worm, which forms the most elevated part of the 
cerebellum. 

The worm is a small, elongated lobe, shorter and much thinner 
than the hemispheres. In animals lower than mammals, it is the 
only part of the cerebellum present. Its transverse ridges give it a 
worm-like appearance. It unites the upper halves of the mesial 
aspect of the hemispheres, their lower halves being separated by an 
antero-postenor groove called the valley or vallecula. The 
upper surface of the worm is called the superior woi'm and the 
lower surface the inferior worm. The superior and inferior sur- 
faces are separated from one another at the posterior end of the 
worm by the great horizontal fissure; anteriorly, the medullary 
stem of the cerebellum separates them. At either end of the 
worm is a notch bounded by the hemispheres, the anterior and 
posterior cerebellar notch. 

The posterior cerebellar notch is occupied by the falx cere- 
belli. A prolongation of the medullary stem of the cerebellum 
issues from the anterior cerebellar notch. That medullary stem 
splits mesially into two laminae: a superior, which forms the su- 
perior medullary velum and three pairs of peduncles, and an 

62 



Hind-Brain. 63 

inferior, which is the inferior medullary velum. Separating at an 
acute angle, the two lamince form the tent and lateral recesses of 
the fourth ventricle. 

The inferior medullary velum is the inferior lamina of the 
medullary stem. It is a short plate of white matter, not more 
than one quarter of an inch long. It ends in a concave border 
from which a sheet of epithelium continues down over the fourth 
ventricle; and together they form the posterior half of the roof of 
that cavity. Laterally, the inferior velum extends to the flocculus 
of the hemisphere, and blends with the middle cerebellar 
peduncle. In the worm it covers the nodulus antero-superiorly. 
It bounds dorsally the lateral recesses of the fourth ventricle. 

The superior lamina of the medullary stem joins the cerebel- 
lum to the pons. The superior lamina is made up of three pairs 
of cerebellar peduncles and the superior medullary velum. They 
are the continuations of the white matter in the medullary center 
of the cerebellum and issue from the anterior cerebellar notch. 

The superior peduncles (crura ad cerebrum) converge as they 
pass forward and upward to the posterior quadrigeminal bodies, 
where they disappear. They are joined to one another by a thin 
plate of white matter, the superior medullary velum, or valve of 
Vieussens; and, with the valve, form the dorsal longitudinal fibers 
of the pons and, as such, the roof and lateral boundaries of the an- 
terior half of the fourth ventricle. Beneath the corpora quadri- 
gemina and aqueduct of Sylvius most of the fibers of the superior 
cerebellar peduncles decussate; and, inclosing the red nucleus of 
the tegmentum, pass into the subthalmic region of the opposite 
side. 

The inferior peduncles of the cerebellum (crura ad medul- 
lam) issue from the cerebellum between the superior and middle 
peduncles. They first run ventrally to the dorsal surface of the 
pons near its posterior border; and then, bending downward and 
backward (a flexion of more than 90 degrees), they converge in 
the posterior areas of the medulla toward the calamus scriptorius. 
They help to bound laterally the posterior half oi the fourth ven- 
tricle. In the medulla they are called restiform bodies. 

The middle peduncles (crura ad pontem) join the cerjbellum 
to the lateral borders of the pons. To the pons they contribute 
the ventral (or superficial) transverse and the middle transverse 
fibers. The middle peduncles are external to the superior and 



64 The Brain and Spinal Cord. 

inferior peduncles, and are opposite the widest part of the fourth 
ventricle. 

Great horizontal fissure — The cerebellum has one great fis- 
sure which divides it into upper and lower half or suface. The fis- 
sure is shaped like a horse-shoe; its extremities are located on 
either side of the medullary stem, from which the fissure runs 
backward, dividing the border of each hemisphere and the poste- 
rior end of the worm. In the great horizontal fissure the remain- 
ing important fissures of the cerebellum terminate. They are 
nearly parallel with one another; hence, the cerebellum is lami- 
nated, not convoluted like the cerebrum. The extremities of the 
great horizontal fissure are separated from the fourth ventricle by 
a sheet of epithelium, on either side, uniting the borders of the 
superior and inferior medullary laminae, and bounding externally 
the lateral recess. 

SUPERIOR SURFACE OF THE CEREBELLUM. 

The superior surface of the cerebellum is bounded by the great 
horizontal fissure and the superior lamina of the medullary stem. 
It is divided into five continuous lobes by four crescentic fissures, 
called interlobular fissures. 

Fissures— The interlobular fissures divide the worm and both 
hemispheres; and each lobe is composed of a central and two lat- 
eral portions, called lobules. These fissures are named in accord- 
ance with their relation to the lobules in the worm, viz.: 

(i) The precentral fissure, which is located in the anterior 
cerebellar notch. It is between the ltngula and lobulus cen- 
tralis, in the worm; between the fraenulum and ala, in the hemi- 
sphere. 

(2) The postcentral fissure, in the worm, separates the lobu- 
lus centralis from the culmen; and, in the hemisphere, the ala 
from the anterior crescentic lobule. The fissure follows the ante- 
rior border of the superior surface. Both central fissures termi- 
nate on the dorsum of the superior medullary lamina. 

(3) Preclival fissure— Behind the culmen and anterior cres- 
centic lobules is the preclival fissure. It bounds the clivus and 
posterior crescentic lobules in front. 

(4) The postclival fissure is located in the posterior cere- 
bellar notch, from which it curves outward and forward in the 
superior surface of the hemispheres. It separates the clival lobe 



Hind-Brain. 65 

from the folium cacuminus, in the worm, and from the postero- 
superior lobules in the hemispheres. 

Fissures and Lobules of the upper surface of the cerebellum 
from before backward: 

Hemisphere. Worm . Hemisphere. 

Fraenulum. Lingula. Fraenulum. 

Precentral fissure. 
Ala. Lobulus centralis. Ala. 

Postcen tra I fissu re. 
Anterior crescentic. Culmen. Anterior crescentic. 

Preclival fissure. 
Posterior crescentic. Clivus. Posterior crescentic. 

Postclival fissure. 
Postero-superior. FoUum cacuminis. Postero-superior. 

Great horizontal fissure. 

Lobes of superior surface. — These include the divisions of 
the worm and of the hemispheres, and are five in number. 

Lingula and fraenula (Lobus lingulae). — The lingula is a very 
small lobule entirely concealed in the anterior cerebe lar notch by 
the overhanging central lobule. It is a tongue-shaped group of four 
or five rudimentary transverse laminae. It rests upon the superior 
medullary velum,wiih which its white center is continuous. Later- 
ally, the lingula tapers off and is represented, if at all, in the 
hemisphere by a very thin folium called the frcenulum. The 
fraenulum is bounded by the superior cerebellar peduncle, in f<ont, 
.and by the precentral fissure behind. The precentral fissure 
separates the lobe of the lingula from the following: 

Central lobule and alse (Lobus centralis). — The lobulus cen- 
tralis is situated between the precentral and postcentral fissures 
in the anterior cerebellar notch. It covers the lingula and in turn 
is overhung by the culmen. Four or five transverse laminae make 
it up. On section, it is seen to form a single leaf of the medullary 
stem (arbor vitae). The laminae of the central lobule, continuing 
into either hemisphere, form a triangular or wing-like lobule, the 
ala. 

Culmen and anterior crescentic lobules (Lobus culminis) 
— In the culmen the surface of the cerebellum .reaches its highest 
elevation. It is a large lobule and occupies more than half of the 
upper surface of the worm. It is made up of three or four promi 
nent laminae, which extend laterally into the hemispheres and 



66 The Brain and Spinal Cord. 

there form the antei'ior crescentic lobules. The latter occupy 
about one-third of the upper surface of the hemispheres. The 
preclival fissure separates the culmen and anterior crescentic lob- 
ules (the lobe of the culmen) from the lobus clivi. 

Clivus and posterior crescentic lobules (Lobus clivi) — The 
clivus forms the posterior slope, as the culmen forms the summit, 
of the monticulus cerebelli. The clivus has about half the extent 
of the culmen. Its laminae are continued into either hemisphere, 
where they form the large posterior crescentic lobule. The 
increased size in the hemisphere is due to the expansion of the 
secondary folia found in the worm. The anterior and posterior 
crescentic lobules constitute the quadrate lobe, which forms the 
anterior two-thirds of the superior surface of the hemisphere. 
The clivus and its hemispherical extensions are inclosed between 
the preclival and postclival fissures. 

The folium cacuminis and postero-superior lobules (Lo- 
bus cacuminis) lie behind the postclival and in front of the great 
horizontal fissure. The folium cacuminis is the terminal lamina 
in the superior worm, and occupies the posterior cerebellar notch. 
It is beset with rudimentary folia, which are largely developed in 
the hemispheres. The postero-superior lobule is, therefore, very 
large in comparison with the folium cacuminis. It expands later- 
ally to the external border of the hemisphere, where it comprises 
a third of the antero-posterior diameter. The postero-superior 
lobule forms the whole posterior border of the hemisphere. 

INFERIOR SURFACE OF THE CEREBELLUM. 

The inferior surface of the cerebellum is prominent laterally 
and depressed centrally (as the organ is viewed inverted), the 
hemispheres being separated by the antero-posterior vallecula. 
The valley is occupied by the inferior worm and is bounded on 
either side by a small fissure, between the worm and the over- 
hanging hemisphere, called the sulcus vallecula. The inferior 
cerebellar surface is limited by the great horizontal fissure and 
the medullary stem of the cerebellum. It is more complex than 
the superior surface; and its fissures are more sharply curved 
forward as they pass from the worm into the hemispheres. 

Fissures of lower surface— The interlobular fissures of this 
surface are very deep. They are three in number, viz.: the Post- 
nodular fissure in the anterior end of the worm between the 



Hind-Brain. 67 

nodule and uvula; the Prepyramidal fissure between the uvula 
and pyramid; and the Postpyramidal fissure between the pyramid 
and tuber valvulae. 

The postnodular fissure, in the hemisphere, winds forward 
and outward between the inferior medullary velum and the tonsil, 
and then continues laterally between the flocculus and digastric 
lobule to the anterior end of the great horizontal fissure. 

The prepyramidal fissure is very concave. It curves outward 
and forward around the tonsil, separating it from the digastric 
lobule. It terminates behind the flocculus in the postnodular 
fissure. 

The postpyramidal fissure is near the posterior end of the 
worm. It forms an oblique groove in either sulcus vallecula, 
from which three concentric fissures extend into the hemispheres' 
The anterior of the three (the pregracile), usually considered the 
postpyramidal fissure in the hemisphere, separates the digastric 
lobule from the postero-inferior lobule; the remaining two (mid- 
gracile and postgracile) subdivide the postero inferior lobule into 
anterior and posterior slender and inferior semilunar sub-lobules. 
The last is bounded behind by the great horizontal fissure. 

Fissures and lobules of the lower surface of the cerebellum, 
from before backward: 

Hemisphere. Worm. Hemisphere. 

Flocculus. Nodule. Flocculus. 

Postnodular fissure. 
Tonsil. Uvula. Tonsil. 

Prepyramidal fissure. 
Digastric lobule. Pyramid. Digastric lobule. 

Postpyra7nidal fissure. 

Postero-inferior lobule. Tuber valvule. Postero-inferior lobule. 

Great horizontal fissure. 

Lobules of lower surface -They are not continuous with one 
another from the worm to the hemisphere as on the upper surface. 
Excepting the posterior lobules, only a small ridge beneath the 
sulcus valleculae joins them together. The inferior lobes are four 
in number. Each is composed of a central and two lateral 
lobules The lobule in the worm gives the name to the lobe. 

Nodule and flocculi (Lobus noduli)— The nodule is a small 
lo v ule at ihe aut -nor end of the inferior worm. It is composed of 
three or four laminae, which project from the middle of the lower 



68 The Brain and Spinal Cord. 

surface of the inferior medullary velum. Though larger, it is the 
counterpart of the lingula on the superior velum. It is bounded 
by the sulcus valleculas on either side. The inferior medullary 
velum extends laterally from the nodule, and merges with the 
middle peduncle of the cerebellum. In front of the tonsil, a fold 
of gray matter (peduncle of flocculus) appears on the velum. 
That gray matter enlarges more externally to a tufted mass 
called the flocculus. The flocculus is separated from the tonsil 
and digastric lobule by the postnodular fissure. (The whole line 
of structures, viz., the nodule, velum, peduncle and flocculus, form 
the lobe of the nodule). 

Uvula and Tonsils (Lobus uvulae) — The uvula comprises a 
considerable part of the lower worm behind the nodule. It 
broadens backward and is widest next the pyramid. Bounded on 
either side by the sulcus valleculas, it projects into the valley like 
the uvula into the isthmus of the fauces. Three moderate sized 
laminae and six or eight small folia make up the uvula. A slight 
ridge, the fin-rowed band, joins it to the tonsil in the hemisphere. 
From the furrowed band the tonsil expands downward and back- 
ward forming a lobule of nearly a dozen sagittal laminae. The 
tonsil (or amygdala) overhangs the side of the uvula and conceals 
the furrowed band, mesially; and, behind, it conceals the connect- 
ing ridge between the pyramid and digastric lobule. The fossa 
containing the tonsil is the bird's nest (nidus avis). Behind the 
uvular lobe, composed of the above three lobules, are the pre- 
pyramidal fissure and the lobe of the pyramid. 

Pyramid and digastric lobules (Lobe of the pyramid)— As 
seen from the surface, three or four distinct laminae make up the 
pyramid, which is the most prominent lobule of the inferior worm. 
A low connecting ridge joins the pyramid to the digastric lobule 
in the hemisphere. The digastric (or biventral) lobule is triangu- 
lar in outline. Its base looks toward the flocculus and is bounded 
by the postnodular fissure; its apex is continuous with the con- 
necting ridge. The laminae composing it radiate from the apex 
toward the base, and are divided into two groups by a very deep 
intralobular fissure. The postpyramidal fissure bounds it postero- 
external^, and separates it from the postero-inferior lobule. 

Tuber valvulse and postero=inferior lobule (lobus tuberis)— 
The tuber valvules forms the posterior end of the inferior worm. 
It resembles the lobules of the upper worm, because its half dozen 



Hind-Brain. 69 

tertiary laminae are continued into the hemispheres, the sulcus 
valleculas not cutting them off. The great horizontal fissure sepa- 
rates it from the folium cacuminis of the superior worm. The 
postero-iiiferior lobule comprises the posterior two- thirds of the 
inferior surface of each hemisphere, extending from the digastric 
lobule to the posterior border. Twelve to fifteen laminae compose 
the lobule. They are divided into three groups by the midgracile 
and postgracile fissures; the groups are named the anterior slen- 
der, or pregracile posterior slender, or postgracile, and inferior 
semilunar. The inferior semilunar sublobule, only, is continuous 
with the laminae of the tuber. 

INTERIOR. 
GRAY MATTER OF THE CEREBELLUM. 

The gray matter of the cerebellum is composed of cortex 
which covers the cerebellar laminae and ganglia imbedded in the 
medullary center. 

I. CORTICAL GRAY MATTER. 

The cortex of the cerebellum is made up of two microscopic 
layers, viz., (1) a superficial, or gray cellular layer, and (2) a deep, 
or rust-colored granular lay er. 

(1) Superficial, or gray cellular layer— Thickest on the lami- 
nae and thinnest beneath the fissures is this layer. It contains 
small spheroidal cells and Jarge fl isk-like cells, the cells of Pur- 
kinje; and a very close network of fibers. 

Cells — Purkinje's cells are located near the deep surface of the 
cellular layer. Each has one axon, which, after piercing the gran- 
ular layer, becomes a fiber of the medullary center ( a projection 
fiber). From the outer end of each cell antler like, protoplasmic 
processes (dendrites) are given off; they ramify toward the sur- 
face in a plane at right angles to the intralobular fissures. The 
spheroidal ceils form an outer and inner layer. They have rich 
dendritic processes and one axis cylinder each. The dendrites 
ramify throughout the cellular layer. In the outer layer the sphe- 
roidal cells are smaller than in the inner layer. Their axis-cyl- 
inders run parallel with the surface and witn the intralobular fis- 
sures. They branch freely and terminate in a manner unknown. 
The cells of the inner layer are called "basket cells". Their axis- 
cylmders processes are parallel with the former. They give off 
vertical branches which descend to Purkinje's corpuscles and in- 
close them in a basket work of filaments. 



yo The Brain and Spinal Cord. 

Fibers of the gray cellular layer have three sources: (a) 
the dendritic and axonic processes of cells within the layer; (b) 
processes of cells in the granular layer, viz., the neurogliar fibers 
of Bergmann (vertical), which extend from the glia cells in the 
granular layer outward to the surface of the lamina, where they 
form beneath the pia mater a feltwork like the limiting mem- 
branes of the retinas; and the axons of the granule-cells, whose 
T-branches form horizontal fibers in the cellular layer; and (c) 
fibers of the medullary center (projection fibers) arise or end in 
the cellular layer. Purkinje's corpuscles originate a part of the 
projection fibers. Others, perhaps arising in the spinal cord, end 
either as arborizations about the dendrites of the cells of Purkinje 
or as moss-like apendages (Ramon y Cajal) in both granular and 
cellular layer. 

(2) The deep or rust=colored granular layer is of uniform 
thickness. It blends centrally with the medullary stem.. 

Cells of the granular layer— The granules are small, round 
cells, closely packed externally, but scattered among the projec- 
tion fibers centrally. Each granule has one axon. It runs out 
into the cellular layer, branches T-l ike, and forms many of its 
horizontal fibers. Dendritic processes are abundant. They 
ramify chiefly within the granular layer. The neurogliar cells y 
which originate the fibers of Bergmann, lie near the cells of Pur- 
kinje. 

Among the fibers of the granular layer are included the pro- 
cesses of the granules and glia cells, and the projection fibers. 

11. ganglionar gray matter. 

The ganglia of the cerebellum are the corpus dentatum and the 
three nice lei of Stilling, 

The corpus dentatum is a wavy pouch of yellowish-brown 
gray matter, imbedded in the medullary stem of each hemisphere. 
It is filled with white fibers, which issue from its anterior, open 
end; and form the greater part of the superior cerebellar pe- 
duncle. Stellate nerve cells (from 6 micromes to 10 micromes in 
diameter) are the essential element of both the corpus dentatum 
and Stilling's nuclei. 

Nuclei of Stilling — One of these, a club-shaped mass, the 
nucleus e?nbolifor?n us, partly closes the mouth ot the dentate body. 
Mesial to that, is an elongated antero-posterior ganglion, bulbous 



Hind-Brain. 71 

behind, called the nucleus globosus . The third nucleus is in the 
anterior end of the worm, just above the tent of the fourth ventri- 
cle. It is called the nucleus of the roof, nucleus fastigii. In the 
two last the stellate cells are larger than in the nucleus emboli- 
formis or corpus dentatum; but, otherwise, they are alike in 
structure. 

WHITE MATTER OF THE CEREBELLUM. 

The white matter of the cerebellum is arranged in three sys- 
tems similar to that of the cerebrum. 

I. Projection, or Peduncular fibers. 
II. Commissural fibers. 
III. Association fibers. 

I. PROJECTION FIBERS. 

These include all fibers of the medullary stern as it issues from 
the anterior cerebellar notch. They are in continuity with the 
white center of the cerebellum, called the arbor vilce. Dividing 
mesially into a supericr and an inferior la77iina (united laterally), 
the medullary stem forms the tent and lateral recesses of the 4th 
ventricle. The inferior lamina is the inferior medullary velum, 
whose fibers pass into the nodule and flocculi. The superior 
lamina forms the superior medullary velum and three pairs of 
cerebellar peduncles. 

Superior peduncles — Three bundles of fibers make up the 
superior peduncles. One small bundle issues from the worm 
and a very la-ge one from the corpus dentatum. The latter 
forms most of the peduncle. The third bundle (a small one) arises 
in the cerebrum and passes through the arbor vitas external to 
the dentate bo^y, terminating in the cortex. The superior 
medullary velum arches over the 4th ventricle between the 
superior peduncles. It is composed chiefly of longitudinal fibers 
running between the worm and the cerebrum. One distinct bundle, 
derived from the spinal cord, passes through it to the worm. It is 
the antero-lateral ascending cerebellar tract. The decussating 
root-fibers of the fourth nerve (pathetic) course transversely 
through the superior velum. 

Middle peduncles — They pass to the pons and form its ventral, 
or superficial, t'ansverse and its middle transverse fibers. The 
fibers of the middle peduncle arise from every part of the hemi- 
sphere cortex perhaps a few from the worm. They cross one 



72 The Brain and Spinal Cord. 

another in the peduncle — fibers from the anterior part of the hemi- 
sphere running to the posterior portion of the pons, and vice 
versa. Passing toward the median line, most of the fibers end in 
the nuclei pontis of the same side; a few end in the opposite 
nuclei. Of the remaining fibers, some run upward to the cere- 
brum and others down into the spinal cord. These fibers become 
longitudinal in the pons both on the same and on the opposite side 
of the median line. They run upward with both crustae, but 
chiefly with the opposite one; and they accompany the fillet and 
posterior longitudinal bundle of the same side to the nuclei of the 
third, fourth and sixth cranial nerves. 

The inferior peduncles can be traced to the upper part of the 
hemispheres and to the worm. Inferiorly, they become the resti- 
form bodies of the medulla oblongata. The bundles of compo- 
nent fibers are very numerous: (i) The direct cerebellar tract, 
terminating in the worm; (2) external arciform fibers of the 
medulla; (3) internal arciform fibers from the opposite lower 
olive; (4) accessory cuneate bundle of same side; (5) anterolateral 
descending cerebellar tract; and (6) the bundle of Solly from the 
antero-lateral tract of the spinal cord. (Also fibers of the 3d, 5th, 
6th, 8th and 12th cranial nerves and of the anterior roots of the 
spinal nerves. — Marchi.) 

11. commissural fibers. 
The cerebellar hemispheres are joined by transverse fibers, of 
which there are two sets, namely: One near the anterior end of 
the worm beneath the central lobe, and the other at the posterior 
end of the worm. 

HI. ASSOCIATION FIBERS. 

Antero-posterior fibers join the cerebellar laminae to one an- 
other. They arch beneath the fissures, and remain in one hemi- 
sphere 

BLOOD SUPPLY OF CEREBELLUM. 

Three pairs of arteries supply the cerebellum. The superior 
cerebellar, from the basilar; the anterior inferior cerebellar, from 
the same; and the posterior inferior cerebellar, from the verte- 
bral. 

Three sets of veins carry the blood away. The superior cere- 
bellar veins pour their blood against the current into the straight 
sinus. The inferior cerebellar veins empty in like manner into 



Hind-Braix. 73 

the lateral sinus; and the lateral cerebellar veins, into the supe- 
rior petrosal sinus. 

The trunks of both veins and arteries ramify in the pia mater. 

The Pons Varolii. 

The pons is the ventral part of the hind-brain, the cerebellum 
being its dorsal portion. The pons is developed from the floor of 
the epencephalon. It is so named because it forms the connect- 
ing link, or bridge, between the mid-brain, above, and the cere- 
bellum and medulla oblongata, below; between the medulla and 
cerebellum, and between the two cerebellar hemispheres. 

In shape the pons is roughly cylindrical. A corond section of 
it resembles an inverted transverse section of the penis. Its ven- 
tral surface presents a mesial longitudinal groove, the sulcus bas- 
ilaris, along which runs the basilar artery. The dorsal surface is 
rendered prominent in the mesial line by the superior cerebellar 
peduncles and valve of Vieussens, which extend from the cere- 
bellum forward to the corpora quadrigemina. 

Size— The pons is about one inch long. It is a little broader 
than long, and measures three-quarters of an inch, dorso-ven- 
trally. 

Position- It rests in the anterior end of the groove which ex- 
tends from the foramen magnum to the dorsum sellae ; and lies be- 
tween and ventral to the hemispheres of the cerebellum. Supe- 
riorly, it j uns the mid-brain; and behind it is continuous with the 
medulla oblongata. 

Surfaces of the Pons— The pons has four surfaces, viz., 
superior (attached); i7iferior (attached); ventral (free), and dor- 
sal (free); and two borders, namelv, right and left lateral, contin- 
uous with the middle peduncles of ihe cerebellum. 

The superior and inferior surfaces are made by section; and 
are directly continuous, by the longitudinal fibers of the pons, with 
the mid-brain above and medulla below. 

Ventral surface (Tuber annulare)— The ventral surface of the 
pons looks downward and forward ; and rests on the sphenoid bone 
behind the sella Turcica. It is divided into lateral halves by the 
groove for the basilar artery. Antero-posteriorly the surface is 
slighdy convex, and it is markedly so from side to s de. It shows 
transverse striations, which converge laterally, due to the fibers 
that form it, and enter the middle peduncles of the cerebellum. 



74 The Brain and Spinal Cord. 

Not all the fibers of the tuber annulare are exactly transverse in 
direction. Those at the anterior end of the pons are arched, con- 
vex forward, and form a rounded margin, which covers the lower 
part of the crustse of the mid-brain: at the posterior extremity of 
the pons, the fibers are convex backward and partially conceal the 
pyramids of the medulla oblongata. The two roots of the 5th 
nerve (trifacial) issue from the lateral border (Henle) of this sur- 
face, a little in front of the middle. 

The dorsal surface of the pons is concealed by the cerebellum. 
It presents a medium longitudinal elevation due to the superior 
peduncles of the cerebellum and valve of Vieussens. The pedun- 
cles converge forward and upward and run beneath the posterior 
quadrigeminal bodies of the mid-brain. The valve spans the in- 
terval between the peduncles; and forms the floor of the slight 
groove which separates them. A low and narrow ridge runs 
from the corpora quadrigemina down the mi Idle of the valve. It 
is called the frenulum. Each lateral portion of the dorsal surface 
is depressed. Or this depressed portion, the lower fillet produces 
a low ridge which, trending upward and toward the median line, 
winds over the anterior end of the superior cerebellar peduncle 
a nd terminates at the posterior corpus quadrigeminum. This 
ridge is joined by a much slighter one, which runs from the valve 
outward and forward over the posterior end of the superior pe- 
duncle; it is caused by a bundle of fibers from theantero-lateral as- 
cending cerebellar tract. In the superior medullary velum (or 
valve of Vieussens) the 4th cranial nerve decussates; and then, 
issues from its lateral portion on each side of the fraenulum. 

WHITE MATTER OF THE PONS. 

The pons is composed of transverse and longitudinal white 
fibers and of gray matter. The transverse fibers are found in the 
ventral portion of the pons; the longitudinal, in the dorsal part 
and also intersecting the middle transverse fibers. 

TRANSVERSE FIBERS OF PONS. 

The transverse fibers form three consecutive layers in the ven- 
tral area of the pons, viz., the ventral, the middle, and the dorsal 
layer. They lie one upon another. 

The ventral transverse fibers (superficial transverse) form a 
thin layer constituting the tuber annulare, or ventral surface of 
the pons. 



Hind-Brain. 75 

fliddle transverse fibers (ventral deep-transverse). — These 
form a thick lamina dorsal to the ventral transverse fibers and in 
contact with the ventral lamina. They are intermingled with 
longitudinal fibers running from the crustae (middle third) down 
to the pyramids of the medulla oblongata. In the meshes between 
the intersecting fibers are masses of gray matter called the nuclei 
pontis. The middle and ventral transverse fibers form the mid- 
dle cerebellar peduncle. Tracing the fibers from the cerebellum 
they appear to end, for the most part, in the nuclei pontis of the 
same side. Some of them turn upward toward the cerebrum, 
both on the same and on the opposite side (with the pyramidal 
fibers, posterior longitudinal bundle and fillet); and others accom- 
pany the pyramids and posterior longitudinal bundles into the 
spinal cord. 

The dorsal transverse fibers (dorsal deep-transverse) com- 
pose a thin layer on the dorsum of the middle transverse and py- 
ramidal fibers, separating them from the formatio reticularis. The 
dorsal transverse lamina is best marked in the posterior part of 
the pons, where it is called the trapezium. Its fibers converge lat- 
erally to the accessory auditory nucleus and lateral root of the 
auditory nerve, some of them passing into the superior olivary 
nucleus. Mesially, the fibers of the trapezium decussate in the 
raphe; and many of them pass with the lower fillet to the poste- 
rior quadrigeminal body. Thus are the posterior corpora quad- 
rigemina connected with the 8th cranial nerves. 

LONGITUDINAL FIBERS OF PONS. 

Like the transverse, the longitudinal fibers of the pons are ar- 
ranged in three distinct laminae, viz., the ventral, the middle and 
the dorsal. The last two are in contact with one another in the 
dorsal area of the pons; but the ventral lamina is separated from 
the middle by the trapezium. 

The ventral longitudinal fibers (ventral deep-longitudinal) 
are the pyramidal fibers. They run from the middle third of 
each crusta down through the middle transverse layer of the pons 
to the pyiamids of the medulla oblongata. They form a thick 
bundle on either side the median line, which presses down the 
ventral transverse fibers and produces the sulcus basilaris. The 
ventral longitudinal fibers are to a small extent made up of fibers 
from the middle cerebellar peduncles (chiefly from the opposite 



j6 The Brain and Spinal Cord. 

one), which run both to the cerebrum and to the spinal cord. 
The nuclei pontis are scattered among them. 

Middle longitudinal fibers (dorsal deep-longitudinal)— These 
are contained in the formatio reticularis. They are dorsal to the 
trapezium, and lie in the floor of the fourth ventricle. Laterally, 
the lamina is in contact with the dorsal longitudinal layer; but, 
mesially, the two are separated from one another by the fourth 
ventricle. The middle longitudinal fibers are mingled with many 
oblique fibers; and, thus, there is produced the net-like arrange- 
ment suggesting the name, formatio reticularis. In the pons, the 
formatio reticularis is a continuation of the same lamina in the 
medulla oblongata. Considerable gray matter is found in its 
meshes, especially in the part next the fourth ventricle. The for- 
matio reticul iris contains three distinct bundles of longitudinal 
fibers: the fillet, the posterior longitudinal bundle and the ascend- 
ing root of the trifacial nerve, (Also the funiculus teres) 

The fillet fibers form a broad, flat bundle next the trapezium. 
The width of the bundle is almost equal to half the transverse 
axis of the pons: the lower fillet lies just beneath the dorsal sur- 
face; and the mesial runs along the raphe. Anterior to the pons 
we have the upper, lower and mesial fillet, which have been traced 
through the tegmentum of the mid-brain. (See Mid-brain.) 

Posterior longitudinal bundle— -It is a small funiculus situated 
near the raphe, and just beneath the gray matter in the floor of the 
fourth verticle. It is continued down into the anterior column of 
the spinal cord without decussation. In the pons, fibers join it 
from the cerebellum by the middle peduncle, and from the nucleus 
of the abducens (or 6th) nerve. Both the posterior longitudinal 
bundle and fillet enter the tegmentum of the mid-brain, where 
they have already been traced. 

Ascending root of the trifacial (or jth) nerve (accessory sen- 
sory root) — It is a small bundle of fibers which begins near the 
tubercle of Rolando in the medulla oblongata. It runs forward 
close to the lateral part of the floor of the fourth ventricle and 
joins the main sensory root ventral to the superior cerebellar 
peduncle. 

The dorsal longitudinal fibers (superficial longitudinal) form 
the mesial portion of the dorsa.1 surface of the pons. They bound 
laterally and form the roof of the anterior half of the fourth ven- 
tricle. The dorsal longitudinal fibers compose the superior 



Hind-Brain. yj 

peduncles of the cerebellum and the valve of Vieussens. The 
pedunclts rest on the formatio reticularis. Between them the 
valve arches over the fourth ventricle, 

GRAY MATTER OF THE PONS. 

In the pons gray matter is found in two situations: (i) in the 
interstices between the middle transverse and ventral longitudi- 
nal fibers, the nuclei pontis ; and (2) in the formatio reticularis 
or floor of the fourth ventricle. 

The nuclei pontis are small masses of gray matter containing 
multipolar nerve cells. They receive many fibers from the cor- 
responding middle peduncle of the cerebellum and a few from 
the opposite peduncle; and they probably originate the fibers of 
the outer third of the crusta. 

The gray matter of the formatio reticularis includes the 
superior obve, and the nuclei of the fifth, sixth and seventh cranial 
nerves and a part of the dorsal nucleus of the auditory nerve. 
The nerve nuclei will be further noticed in the description of the 
fourth ventricle. 

Superior olivary nucleus — It is situated in the lateral part of 
the formatio reticularis, just dorsal to the trapezium. It contains 
sm ill nerve cells, and, in this respect, resembles the o'ive of the 
medulla. In size it is microscopic. Fibers may be traced from it 
to the opposite accessory auditory nucleus by way of the trape- 
zium. It thus helps to form the latter. 

BLOOD SUPPLY OF PONS. 

The vertebral, basilar, posterior cerebral and superior cerebel- 
lar arteries supply the pons. 



THE AFTER-BRAIN OR MEDULLA OBLON- 
GATA. 



The medulla oblongata is the distal, or caudal, part of the 
brain. It may be regarded as the expanded intracranial portion 
of the spinal cord, hence the synonym, spinal bulb. Situation. 
It occupies the basilar groove of the occipital bone, posterior to 
the pons; and is continuous with the spinal cord through the 
foramen magnum. Dorsally, it is in part concealed in the valley 
of the cerebellum. The vertebral arteries wind forward around it, 
and form the basilar at its junction with the pons. 

Size— The medulla is about an inch long, and dorso-ventrally, 
is half an inch thick. Its width at the lower end is half an inch, 
also. At the upper extremity it is three-quarters of an inch wide. 

Its shape resembles an inverted frustum of a cone flattened 
dorso-ventrally at the base. The truncated apex of the frustum, 
which is nearly circular in outline, is continuous with the spinal 
cord; and the flattened base joins the pons Varolii. On the ventral 
surface, a transverse groove marks the boundary between the 
medulla and pons. The medulla oblongata is a bilateral organ 
composed of symmetrical halves. In the interior, the two halves 
are united bv both gray and white matter in the raphe, but on the 
surface they are partially separated by the anterior and the pos- 
terior median fissure. These fissures are continuations of the 
same in the spinal cord, but neither extends the whole length of 
the medulla. The anterior median fissure is interrupted in the 
lower part of the medulla by the crossing of two large tracts of 
fibers, forming the decussation of the pyramids ; while only through 
the lower half of the medulla does the posterior median fissure 
extend. 

Origin— The medulla oblongata is developed from the meten- 
cephalon of the embryo. The metencephalic floor and lateral 
walls thicken and form the greater part of the medulla. Poste- 
riorly, the roof undergoes some thickening; but it stretches out to 

78 



After-Brain. 79 

a single layer of epithelium, anteriorly, which is continuous at its 
upper end with the inferior medullary velum of the cerebellum. 

Ventricle —The common cavity of the fourth and fifth brain 
vesicles persists in the mature brain as the fourth ventricle. The 
fourth is, therefore, the ventricle of the adult .hind-brain and 
after-brain. 

SURFACES. 

The medulla oblongata presents four surfaces: the ventral, 
dorsal and two lateral, separated by the ventro-lateral and dorso- 
lateral grooves . In the upper medulla, the surfaces are clearly 
defined; but they become less distinct as they descend to the pos- 
terior and nearly circular extremity. 

The ventro= lateral groove separates the ventral from the lat- 
eral surface, and is in line with the exit of the anterior roots of 
the spinal nerves. No corresponding groove exists in the cord. 
From the ventro-lateral groove issue the roots of the hypoglossal 
nerve. The abducens (or 6th) nerve arises in line with it from 
the transverse groove between the pons and medulla. 

Dorsolateral groove— The postero-lateral fissure of the spinal 
cord, continued into the medulla, becomes the dorso-lateral 
groove. Through the fissure in the cord, pass the posterior roots 
of the spinal nerves; from the groove in the medulla, arise the 
accessory root of the nth and the roots of the 10 h and 9th cranial 
nerves. The 7th cranial nerve and the mesial root ot the 8th 
arise together at the anterior end of the groove. The last two 
come out between the medulla and pons. The dorso-lateral 
groove is not parallel with the axis of the medulla, but bends out- 
ward and forward as it ascends. Interiorly, it is obliterated for a 
short distance by the crossing of the direct cerebellar tract from 
the lateral to the posterior surface. It separates the lateral from 
the dorsal ^rface. 

The ventral surface of the medulla, bounded on either side by 
the ventro-lateral groove, extends from the transverse sulcus 
behind the pons down to the spinal cord. It is made up of sym- 
metrical halves, united below, by the decussation ot the crossed 
pyramidal tracts; but, separated above, by the anterior median 
fissure, which terminates at the posterior end of the pons in a 
b ind foiamen (foramen caecum of Vicq d'Azyr). On either side 
of the median fissure, the ventral surface presents a fusifo»m 
eminence, most prominent near the pons, called the pyramid. 



8o The Brain and Spinal Cord. 

Two tracts of longitudinal fibers form the pyramid, viz.: the 
crossed pyramidal tract, next the anterior median fissure; and the 
direct pyramidal tract, which runs next the ventrolateral groove. 
Transverse fibers are also seen crossing the pyramid from within 
outward. A small bundle runs near the pjns, called the ponti- 
ciilus of Arnold; and a more or less continuous sheet of fibers, the 
external arc i form fibers, emerges from the anterior median fissure 
and winds around the medulla to the dorsal surface, where its 
fibers enter the restiform body. 

The ventral surface is identical with the surface of the two 
anterior areas of the medulla. 

Lateral surface— There are a right and a left lateral surface. 
Each is bounded by the ventro-lateral and the dorso-lateral 
grooves: and inclosed between the roots of the hypoglossal nerve, 
ventrally, and those of the ninth, tenth and accessory portion of 
the eleventh, dorsally. Lateral surface is synonymous with sur- 
face of the lateral area. The lateral surface is formed, above, by 
the olivary body, below, by the lateral tract, and winding back- 
ward over both, the external arciform fibers. 

The olivary body is an elongated oval eminence, a half inch in 
length, situated just behind the pons. It is produced by the olivary 
nucleus in the lateral area of the medulla; and, superficially, is 
composed of fibers from the antero-lateral ground bundle of the 
lateral tract. 

Lateral tract — It is made up of three bundles of fibers: the 
antero-lateral ground bundle, which, splitting into a superficial 
and a deep lamina, incloses the olivary nucleus; the antero-lateral 
descending cerebellar tract, running down the ventro-lateral 
groove; and the antero-lateral ascending cerebellar tract, which 
runs up the dorso-lateral groove. At the junction of the medulla 
with the spinal cord the direct cerebellar tract passes from the 
lateral to the dorsal surface. The external arciform fibers may 
be so numerous as to conceal the lateral tract and lower part of 
the olive. 

The dorsal surface of the medulla comprises all the surface 
inclosed between the diverging dorso-lateral grooves. It em- 
braces the surfaces of the two posterior areas of the medulla. 

Inferiorly, it is divided into lateral halves by the posterior 
median fissure, and presents f jur bundles of fibers in each half. 
From the fissure outward they are as follows: the funiculus 



After-Brain. 8i 

gracilis, funiculus cuneatus, funiculus of Rolando, and the direct 
cerebellar tract. 

The funiculus gracilis is the continuation of the postero-median 
column of the spinal cord, and the funiculus cuneatus and funi- 
culus of Rolando are in direct continuity with the postero-lateral 
column of the cord. These three bundles leave the surface and 
end in the gracile, cuneate and Rolandic nuclei of the medulla. 
The direct cerebellar tract is continued up from the lateral column 
of the spinal cord. Remaining on the surface, it runs up to the 
cerebellum through the restiform body. 

Superiorly, the dorsal surface, on either side, is formed by a 
large rounded band of fibers, the restiform body. Of the superfi- 
cial fibers in the medulla, the direct cerebellar tract, the antero- 
lateral descending cerebellar tract and the external arciform fibers 
are continued into the restiform body. It is also called the infe- 
rior peduncle of the cerebellum. A single layer of flattened epi- 
thelial cells stretches between the two restiform bodies; and roofs 
over the posterior part of the fourth ventricle. It is the roof epi- 
thelium. By it the dorsal surface is completed. 

The roof epithelium, seen in the mid dorsal surface of the me- 
dulla, is of triangular shape; its base is attached to the inferior 
medullary velum of the cerebellum; its apex covers the inferior 
angle of the fourth ventricle; and, laterally, it is attached to the 
clava, the cuneate tubercle and the restiform body. The line of at- 
tachment to the restiform body runs, first, obliquely upward and 
outward; and then, transversely outward, posterior to the lateral 
recess. The borders of the epithelium become thickened by the 
addition of neuroglia, and are in continuity with the ependyma of 
the ventricle. The thickened apex of the epithelial lamina is 
called the obex. With the pia mater investing it, the roof epi- 
thelium forms the posterior choroid tela, which is perforated in the 
median line near its apex, by a foramen, the foramen of Majendie, 
and over each lateral recess by the foramen of Key and Retzius. 
These foramina establish communication between the subarach- 
noid space and the ventricle. On either side of the median line, 
a longitudinal invagination of the epithelial lamina dip? into the 
ventricle; and is occupied by a vascular fold of pia mater, which 
constitutes the choroid plexus of the fourth ventricle. If the roof 
epithelium be torn away, as it usually is with the pia, a rough line 
of separation is seen winding over the restiform body. That line 
is the ligula. Two layers of ependyma form it. 



82 The Brain and Spinal Cord. 

INTERIOR OF THE MEDULLA. 

The medulla is made up of white matter and gray matter, 
which together bound the posterior part of the fourth ventricle. 

WHITE MATTER. 

For the most part the white matter of the medulla is continu- 
ous with the longitudinal fibers of the pons and spinal cord, above 
and below, respectively; and with the inferior peduncles of the 
cerebellum, dorso-laterally. To these add the bulbar roots of the 
eighth to the twelfth cranial nerves, and a number of fibers in the 
raphe to complete the list. 

Formatio reticularis— Superficially,the white matter is collected 
into great bundles of fibers, such as the pyramids, cerebellar 
tracts and restiform body; but, in the deep parts of the medulla, 
the white matter enters into a great network called the formatio 
reticularis, which has gray matter in its meshes and embraces all 
the medulla between the ventricular gray matter, dorsally, and 
the pyramid, olivary nucleus, and restiform body, ventro-later- 
ally. The formatio reticularis contains many scattered fibers 
from the antero-lateral tract of the spinal cord, and two definite 
bundles, viz., the posterior longitudinal bundle and fillet, (see be- 
low). These are all longitudinal in direction. Transverse fibers 
are also very numerous. They are made up of the internal arci- 
form fibers (q. v.) and dendritic processes of cells in the meshes 
of the network. In the formatio reticularis is much gray matter 
which may be considered as the disintegrated H-shaped column 
continued up from the spinal cord. 

Raphe— Fibers form only a part of the raphe which unites the 
lateral halves of the medulla. The raphe is a sagittal lamina of 
neuroglia containing nerve cells and decussating, dorso-ventral 
and longitudinal fibers, (a) The decussating fibers are chiefly 
the internal arciform. A few are decussating root-bundles of some 
of the cranial nerves (Schafer). (b) Running into the anterior 
median fissure, the dorso-ventral fibers become the external arci- 
form fibers. Traced dorsally some of them are found continuous 
with the acaustic striae in the floor of the fourth ventricle, (c) 
Fibers from both sets of arciform fibers turn up and run longitu- 
dinally for a short distance in the raphe. Their destination is un- 
known. 

The white matter of the medulla is divided by the direction of 



After-Brain. 83 

its fibers into three classes or systems: (1). Transverse fibers; 
(2) Dorso-ventral fibers; and (3) Longitudinal fibers. 

(1) The transverse fibers of the medulla are chiefly the 
external and internal arciform fibers. The former have been 
traced from the anterior median fissure over the ventral and 
lateral to the dorsal surface of the medulla, where they enter the 
restiform body. The internal arciform fibers are contained in the 
formatio reticularis. They are disposed in two groups, viz., those 
of the sensory decussation, and those of the olivary peduncle. 

The fibers of the sensory decussation arise from the nucleus 
gracilis and nucleus cuneatus. Bending ventrally through the 
posterior horn of gray matter, they decussate through the median 
raphe, and then run forward toward the cerebrum as a part of the 
opposite fillet. The sensory or fillet decussation is nearer the 
pons and dorsal to the decussation of the pyramids. 

The olivary peduncle is a sheet of fibers extending between 
the two olivary nuclei of the medulla. Of this lamina, the ante- 
rior and posterior fibers pierce the olivary nucleus and run to the 
cerebellar cortex through the restiform body. They connect 
either hemisphere with the opposite nucleus. A small bundle of 
fibers appears to leave the upper part of the nucleus and run up 
through the formatio reticularis of the pons and the tegmentum 
of the midbrain to the same side of the cerebrum. The last is 
the olivary funiculus. 

(2) The dorso=ventral fibers of the medulla are found in three 
situations: (a) in the raphe, (b) between the anterior and lateral 
areas, and (c) between the lateral and posterior areas. 

(a) The dorso-ventral fibers of the raphe are chiefly the ex- 
ternal arciform fibers. These can be traced to the cerebellum 
through the restiform body, but their origin is uncertain. Some 
of them seem to arise from the arciform nuclei on the ventral 
surface of the pyramids. The root-bundles of eighth to the 
twelfth cranial nerves constitute the remaining groups of dorso- 
ventral fibers. By them the medulla is divided into areas. 

(b) The root-bundles of the hypoglossal nerve run from the 
ventricular gray matter, near the median line, ventro-laterally to 
the ventrolateral groove, where they emerge. Inclosing between 
them and the raphe, the anterior area, they also separate it from 
the lateral area. The anterior and lateral areas are bounded 
dorsally by the thick sheet of gray matter in the floor of the fourth 
ventricle. 



84 The Brain and Spinal Cord. 

(c) The ?nesial root of the auditory nerve, the roots of glos- 
sopharyngeal and vagus and the accessory root of the eleventh 
form the third group of dorso-ventral fibers. From the dorso- 
lateral groove, which is their superficial origin, they may be 
traced through the medulla to ventricular gray matter external to 
the column of cells from which the twelfth nerve arises. They 
separate the lateral from the posterior area. The posterior area 
comprises everything dorsal to the above roots of the eighth to 
eleventh cranial nerves. It thus includes the gray matter in the 
floor of the fourth ventricle. 

(3) Longitudinal fibers— In the medulla, the longitudinal 
fibers are chiefly continuations of the same in the spinal cord. 
They can be best located by reference to the three areas, — Ante- 
rior, Lateral and Posterior. 

ANTERIOR AREA. 

The anterior column of the spinal cord is continued into the 
anterior area of the medulla. A part of it is in continuity with 
the direct pyramidal tract; the remainder, with the formatio retic- 
ularis alba. (It is white because of the scarcity of cells.) The 
direct pyramidal'tract is joined on its mesial aspect by the crossed 
pyramidal tract, and the two constitute the pyramid. The pyra- 
mid occupies the ventral portion of the anterior area. It is com- 
posed of the axons of co/tical cells in the Rolandic region of the 
cerebrum; and diminishes in size as it descends through the pons 
and medulla, because some of its fibers terminate in ramifications 
about the cells of cranial nerve-nuclei. In the lower part of the 
medulla, the pyramid breaks up into the direct pyra?7iidal tract, 
which descends along the anterior median fissure in the same side 
of the spinal cord; and the crossed pyra77iidal tract, which after 
decussating with its fellow through the anterior median fissure, 
runs down in the lateral column of the opposite side of the cord. 
The fibers of the direct tract cross in succession to the opposite 
side of the cord (through the anterior or white commissure); and 
there, with the fibers of the crossed pyramidal tract, terminate in 
fibrillar end-tufts abcut the cells in the anterior cornu of gray 
matter. Thus the pyramid forms a cerebral tract for efferent 
(motor) cranial and spinal nerves. 

The deep part of the anterior area is occupied by the formatio 
reticularis alba. Gray matter from the anterior horn is scattered 



After- Brain. 85 

throughout the reticular formation, but it contains very few nerve 
cells and is of a light color. The internal accessory olivary 
nucleus is imbedded in it near the pyramid, and two definite 
bundles of longitudinal fibers have been demonstrated, namely: 
the Fillet and the Posterior longitudinal bundle. 

Fillet— Just dorsal to the pyramid in the anterior area of the 
medulla, is a large bundle of fibers called the fillet. The fillet 
arises from the nucleus gracilis and nucleus cuneatus of the me- 
dulla, and from the posterior gray horn ot the spinal cord. M he 
gracile and cuneate fibers cross the median raphe in the medulla 
(sensory decussation): those fibers from the posterior gray horn 
decussate through the white commissure of the spinal cord; and, 
ascending through the antero-lateral column of the cord, join the 
former group in the anterior area of the medulla. As the fillet 
runs brainward through the reticular formation of the pons, it 
receives fibers from the opposite accessory auditory nucleus and 
from the middle peduncle of the cerebellum. It is composed of 
ascending axons which constitute a "cerebral" tract for afferent or 
sensory fibers of spinal nerves and for at least one cranial nerve, 
the auditory. 

The posterior longitudinal bundle is a small funiculus com- 
posed of fibers continued up from the anterior column of the spi- 
nal cord. It runs along the median raphe in contact with the 
ventricular gray matter. In the pons, it is a more distinct bundle; 
and is there augmented by fibers from the middle cerebellar pe- 
duncles and the nucleus of the abducens (6th) nerve. Commis- 
sural for some of the cranial nerves and the cerebellum, the pos- 
terior longitudinal bundle also serves to connect cranial nerve- 
nuclei with one another. (See middle longitudinal fibers of pons 
and tegmentum of mid-brain for further tracing of this bundle 
and the fillet.) 

LATERAL AREA. 

Contents: Superficially, the antero-lateral ground bundle and 
antero-lateral descending and ascending cerebellar tracts; deeply, 
the formatio reticularis; and, between the superficial and deep 
structures, the olivary nucleus and external accessory olivary 
nucleus. 

The gray matter of the formatio reticularis grisea is a part of 
the disintegrated anterior gray horn and, unlike that of the ante- 
rior area, it contains many large nerve cells. In the reticular for- 



86 The Brain and Spinal Cord. 

mation there are embedded two nuclei: the nucleus ambiguus, in 
its dorsal part, next the ventricular gray matter, and the nucleus 
lateralis, which is situated near the lateral surface, dorsal to the 
olive. 

Antero= lateral ground bundle— The whole lateral column 
of the spinal cord, except the crossed pyramidal and direct cere- 
bellar tracts, is continued into the lateral area of the medulla. 
Composed of commissural fibers connecting different segments of 
the spinal cord, the antero lateral ground bundle ascends into the 
medulla, and runs in part beneath and in part superficial to the 
olivary nucleus; beyond the olive it is continued in the formatio 
reticularis grisea. 

The antero = lateral descending cerebellar tract arises in the 
cerebellar cortex. It forms part of the inferior peduncle of the 
cerebellum, through which it reaches the medulla. In the lateral 
area, it descends along the ventro-lateral groove, between the 
olive and pyramid. Fibers from the cerebral cortex are scattered 
through the bundle in the cord, and it has been regarded as apart 
of the direct pyramidal tract. 

Antero lateral ascending cerebellar tract —Taking its origin, 
from the vesicular column of CJark in the spinal cord, it ascends 
mingled with the fibers of the above descending tract, along the 
lateral surface of the cord. It runs along the dorso-lateral groove 
and through the formatio reticularis of the medulla; and 
then, turning backward, it reaches the cerebellar worm 
through the superior peduncle and the valve of Vieus- 
sens. A small bundle of its fibers winds over the superior 
cerebellar peduncle, and joins the lower fillet in its course to the 
posterior quadrigeminal body. The antero-lateral ascending cere- 
bellar tract is closely related to the direct cerebellar tract. Both 
arise from Clark's column near the mesial surface of the base of 
the posterior gray horn. 

POSTERIOR AREA. 

The longitudinal fibers of the posterior area form many bun- 
dles; and the bundles are different in upper and lower medulla. 
The formatio reticularis is small in this area, but is continuous 
througho it it. 

The lower or closed medulla contains: the Funiculus gracilis, 
Funiculus cuneatus, Funiculus of Rolando and Direct cerebellar 



After-Brain. 87 

tract (named from the posterior median fissure outward). In the 
upper or ventricular medulla are: the Restiform body, in the 
surface; and the Ascending root of the fifth cranial nerve, the 
Funiculus s:>liiarius and Funiculus teres in the interior. 

The funiculus gracilis is the superior end of the postero-median 
column (Goll's column) of the spinal cord. Near its extremity it 
expands and forms the clava, and then tapers off and disappears 
along the side of the fourth ventricle. The clava is due to the 
nucleus gracilis, in which the fibers of the column end. Like the 
cuneate column, the funiculus gracilis is composed of ascending 
branches of the posterior roots of the spinal nerves. 

The funiculus cuneatus— It is separated from the posterior 
median fissure by the gracile bundle; and is the continuation of 
the postero-lateral column (Burdach's column) of the spinal cord. 
It ends about the cells of the nucleus cuneatus and accessory 
nucleus cuneatus, which form the cuneate tubercle seen on the sur- 
face. Its fibers are the ascending branches of the posterior roots 
of the spinal nerves. 

Funiculus of Rolando— From the cuneate column, a small 
bundle of fibers, taking a more lateral course, runs over the nu- 
cleus of Rolando and constitutes the funiculus Rolandi. This 
column is not represented in the spinal cord. It terminates in 
the nucleus of Rolando, beneath the restiform body. The nu- 
cleus causes a slight eminence on the surface called the tuber- 
culum Rolandi. 

The direct cerebellar tract in the lower medulla crosses the 
dorso-lateral groove, from the lateral column of the cord to the 
posterior area of the medulla: and, there, ascends to form the 
greater part of the restiform body, the inferior peduncle of the 
cerebellum. It takes its origin from the vesicular column of 
Clark. It ends in the cerebellar worm. 

Restiform body— In the upper medulla, forming the lateral 
part of each posterior area, is a large rounded bundle of fibers, 
called the restiform body. It is the largest bundle in the medulla. 
Forming the inferior peduncle of the cerebellum, it terminates in 
the cerebellar cortex of both the hemisphere and worm. It is 
made up of the following: (1) Direct cerebellar tract; (2) 
External arciform fibers; (3) The anterior and posterior fibers of 
the olivary peduncle; (4) A bundle of fibers from the accessory 
cuneate nucleus; (5) Antero-lateral descending cerebellar tract, 



88 The Brain and Spinal Cord. 

and (6) The bundle of Solly (inconstant), which may be traced 
from the restiform body around the lower medulla to the direct 
pyramidal tract of the same side of the spinal cord. 

The restiform body is inclosed between the mesial and lateral 
roots of the auditory nerve (8th). Ventral to it, and between the 
roots, is the accessory or ventral auditory nucleus; on its lateral sur- 
face, among the fibers of the lateral root, is the lateral auditory 
nucleus. 

The ascending root of the fifth nerve is the accessory sensory 
root. It leaves the main sensory root in the pons; and, running 
down in the lateral portion of the posterior area, it terminates 
ventral to the restiform body about the cells of the nucleus 
Rolandi. 

Funiculus solitarius— It is a small, round bundle imbedded in 
the middle of the ventricular gray matter of the posterior area. 
It forms an accessory sensory root for the ninth and tenth cranial 
nerves. Descending near the main nuclei of these nerves, it ends 
about the cells of the gray matter surrounding it. 

Funiculus teres — On either side of the median line and ex- 
tending almost the whole length of the floor of the fourth ven- 
tricle, is a lozenge-shaped eminence, called the funiculus teres. 
In the pontine part of the ventricular floor, it ends as the emi- 
nentia teres. It tapers off to a point in the posterior angle of 
the ventricle and with its fellow, suggests the name applied 
to that angle, the calamus scriptorius. It is composed of a flat 
band of fibers covering the hypoglossal nucleus, posteriorly, 
and terete nucleus, anteriorly. The ascending portion of the root 
of the facial (or 7th) nerve, and fibers from the formatio reticula- 
ris make up the funiculus teres. 

gray matter. 
The gray matter of the medulla is composed, (1) of that con= 
tinued up from the spinal cord, and (2) of added nuclei not 
represented in the cord. 

(1) By the dilatation of the central canal of the spinal cord 
forming the fourth ventricle, the posterior cornua of the H- 
shaped column of gray matter are pushed outward to a trans- 
verse direction; and the bases of the anterior cornua are brought 
into the floor of the ventricle. The expansion of the canal is 
followed by the decussation of the crossed pyramidal tracts 
through the anterior cornua, and of the bulbar portion of the 



After-Brain. 89 

fillets through the posterior cornua, which disposes the H- 
shaped column, as follows: 

Anterior horn— From the base of the anterior cornu is de- 
rived a column of cells, the hypoglossal nucleus, which lies along 
the median raphe beneath the funiculus teres. The head is 
broken up by the crossed pyramidal tract into the nucleus latera- 
lis, in the lateral area, near the dorso-lateral groove; the nucleus 
ambiguus, a. column of cells, pear-shaped in section, seen in the 
dorsal part of the lateral area, accessory to gth and 10th nerves; 
and a third column which constitutes the main motor nuclei of the 
gth, 10th, and bulbar root of the nth cranial nerves. The gray 
matter of the formatio reticularis alba et grisea belongs to the an- 
terior cornu. It is of a li^ht color (alba) in the anterior area, 
where there are a few cells. In the lateral area, cells are numer- 
ous and the color is gray (grisea). 

The posterior horn is decapitated by the fillet. Its base forms 
a column of cells, external to the hypoglossal nucleus, which con- 
tains the chief sensory nucleus of the 10th, of the 9th and of a part 
of the 8th cranial nerves. The head of the posterior horn forms 
the nucleus of Rolando. That nucleus is the accessory sensory 
nucleus of the trifacial (5th) nerve. In it the ascending root of 
the 5th terminates. The posterior horn furnishes the gray matter 
of the reticular formation of the posterior area. 

It should be noted that the chief nuclei derived from the H- 
shaped column lie in the floor of the fourth ventricle. 

(2) Added nuclei— The medullary gray matter not represented 
in the spinal cord makes up the following nuclei: Nucleus 
gracilis; Nucleus cuneatus; Olivary nucleus and Nuclei of 
external arciform fibers. 

Nucleus gracilis and nucleus cuneatus— Situated near the 
dorsal surface of the medulla, beneath the gracile and cuneate 
bundles whose fibers terminate in them, these two nuclei give 
origin to the fibers of the sensory (or fillet) decussation ; and pro- 
duce, respectively, the clava and cuneate tubercle. The acces= 
sory cuneate nucleus is a continuation of the vesicular column 
of Clark at the base of the posterior gray horn. From it a bundle 
of fibers arises, which runs within the restiform body to the cere- 
bellum. The nucleus gracilis and cuneatus are connected with 
the posterior cornu, but have no representative in the cord. 

The olivary nucleus is a pouch-like collection of gray matter 



go The Brain and Spinal Cord. 

resembling the corpus dentatum of the cerebellum. It is situated 
near the lateral surface of the medulla. It is invested superfi- 
cially and deeply by fibers from the antero-lateral ground bundle. 
Its open hilum looks mesially and is filled with fibers, the olivary 
peduncle, which join it to the opposite olive. On either side of 
the olivary nucleus is an accessory nucleus — the internal accessory, 
in the anterior area, and the external accessory, in the lateral area. 
The olivary nucleus, covered by fibers of the antero-lateral 
ground bundle, forms the olivary body. 

The nuclei of the external arciform fibers are several masses 
of gray matter, containing nerve cells, scattered among the arci- 
form fibers, or beneath them. Of these the largest mass is on the 
ventral surface of the pyramid. 

FOURTH VENTRICLE. 

The common cavity of the hind-brain and after-brain is the 
fourth ventricle. The fourth ventricle is contained in the pons 
and medulla, and is ventral to the cerebellum. It is broadest at 
the junction of the pons and medulla. Above and below that 
junction, it contracts to the size of the aqueduct of Sylvius and 
central canal of the spinal cord, with each of which it is continu- 
ous. Dorsally, it communicates with the subarachnoid space 
through three foramina (Majendie, and Key and Retzius). It is a 
low-roofed cavity with a diamond-shaped floor. Its long axis is 
parallel with the spinal cord, and extends from the anterior ex- 
tremity of the pons to the middle of the medulla. The transverse 
axis coincides with the junction of the pons and medulla. Thus 
the anterior triangle of the floor is formed by the pons; the pos- 
terior, by the medulla oblongata. The fourth ventricle is lined 
with ependyina, which is complete throughout, except in the 
roof of the posterior part where only the epithelial layer is 
present. 

Boundaries— The floor is formed by the pons and medulla. 
The lateral walls (anterior triangle) are formed by the superior 
peduncles of cerebellum; and (posterior triangle) by the inferior 
cerebellar peduncles, funiculus cuneatus and funiculus gracilis, 
The roof is formed by the valve of Vieussens, anteriorly; and the 
inferior medullary velum and roof epithelium, posteriorly. The 
anterior and posterior halves of the roof meet at an acute angle 
and form the tent of the fourth ventricle. On either side, the tent 
extends over the restiform body into the lateral recess. The 



After-Brain. 91 

lateral recess is a tunnel-like extension of the ventricular cavity. 
It is bounded, anteriorly and ventrally, by the inferior cerebellar 
peduncle; dorsally, by the inferior medullary velum; and, poste- 
riorly, by the roof epithelium. The choroid plexuses of the 
fourth ventricle invaginate the roof epithelium and hang from the 
roof in the posterior part of the cavity. 

Floor of the fourth ventricle — Because of the origin of one 
or more roots of the posterior eight (5th to 12th) cranial nerves 
from the floor of the fourth ventricle, it is a very important area. 
A median groove, forming the long axis of the diamond-shaped 
floor, divides it in two lateral halves, which are bisected trans- 
versely by a number of lines, the acaustic stricE. The acaustic 
striae are produced by bundles of fibers which issue from the 
median groove, being continuous with dorso-ventral fibers in the 
raphe. They run outward across the floor of the ventricle, in 
part, to the lateral root of the auditory nerve; but, chiefly, to the 
flocculus. They divide each lateral half of the floor into anterior 
and posterior triangle. 

The anterior triangle of the floor -presents: the Eminentia 
teres, Superior fovea, Locus cceruleus and a part of the Acaustic 
trigone. 

The eminentia teres, the anterior extremity of the funiculus 
teres, is located next the median groove, Beneath it are the nu- 
cleus teres (accessory to 9th and 10th cranial nerves), and nucleus 
of the abducens (6th) nerve. External to it and in front of the 
striae acausticae is a small fossa, 

The fovea superior — The fovea superior is near the lateral 
wall of the ventricle and marks the location of the facial (7th) 
nucleus, which is deeply seated in the pons. Running forward 
and mesially along the wall of the ventricle from the superior 
fovea, is a blue -floored groove called 

The locus cceruleus, which continues to the anterior angle of 
the ventricle. The color of the locus coeruleus is due to the 
substantia ferruginea, a pigmented layer of cells underlying it. 
The principal motor nucleus of the trifacial or fifth nerve lies 
beneath the anterior part of the locus cceruleus. 

Posterior triangle of the ventricular floor— It presents: the 
Hypoglossal trigone, Trigonum vagi (fovea inferior, ala cinerea 
and eminentia cinerea) and most of the Trigonum acaustici. 

The hypoglossal trigone is the posterior half of the funiculus 
teres. Its apex is in the posterior angle of the ventricle, its base 



9 2 



The Brain and Spinal Cord. 



looks forward. The twelfth nerve arises from the column of cells 
covered by it. External to the trigonum hypoglossi and posterior 
to the acaustic striae is the inferior fovea, which forms the apex of 

The trigonum vagi. — The pneumogastric trigone is of a darker 
color than the ventricular floor around it, and is often called the 
ala cinerea. The inferior fovea forms the depressed and anteri- 
orly directed apex of the triangle; its floor rises posteriorly to the 
base, eminentia cinerea, which abuts against the lateral wall of 
the ventricle. The principal nuclei of the glossopharyngeal (or 
9th) and the pneumogastric (or ioth) nerves are situated, respec- 
tively, beneath the fovea inferior and trigonum vagi. 

The trigonum acaustici occupies the lateral angle of the ven- 
tricular floor. It is partly in the anterior triangle, but chiefly in 
the posterior. Inclosed between the trigonum vagi and restiform 
body, its base looks forward and is crossed by the acaustic striae. 
A slight eminence, eminentia acausticce, makes the base of the 
trigone most prominent. Beneath the acaustic trigone is the 
dorsal nucleus of the auditory nerve. 

ORIGIN OF CRANIAL NERVES. 

According to Sommering, there are twelve pairs of cranial 
nerves. Their origins are superficial and deep : — 

Name, Superficial Origin. Deep Origin. 

'Nerves — Oltactory 



i st, Olfactory. 



bulb. 



Tract — Three roots. 

f Nerve— Optic com- 
missure. 



ii 



Gyrus fornicatus. 
Trigonum olfactorii. 
Uncus hippocampi. 



2nd, Optic \ 



Optic thai- '^ 

amus, be- 
neath ex- 
[^ Tract \ ternal and 
internal 
| genicul- 
| ate bodies 



f Outer root — Optic 
thalamus, External 
geniculate body,Oc- 
cipital lobe, Ante- 
rior quadrigeminal 

\ body. 



Inner Root-Optic 
thalamus, Internal 
geniculate body. 



After-Brain. 



93 



3rd, Oculomotor. 



Crus cerebri. 



5th, Trifacial. 



Floor of Sylvian aque- 
duct. 



Motor root--Floor 
of 4th ventricle, and 
Sylvian aqueduct. 



Pons, ventral surface. ^ Sensory root— Un- 
I der superior cere- 
I bellar peduncle in 
| pons, and Nucleus 
I of Rolando. 



( Groove between_ 

6th, Abducent j 

( pons and medulla. 

( Groove between 

7th, Facial ] 

( pons and medulla. 

" ^"M ( Groove between 

8th, Auditory ] 

( pons and medulla. 



Floor of 4th ventricle. 



Floor of 4th ventricle. 

Dorsal nucleus, in 
ventricular floor; 
Ventral and Lateral 
nuclei, ventral and 
lateral to restiform 



body; Raphe (by 
acaustic striae), and 
Posterior quadrige- 
minal body (by tra- 
pezium and fillet). 



9th, Glossopharyngeal 

ioth, Pneumogastric. 
nth, Spinal accessory 



Dorso-lateral groove 

of medulla. 

Dorso lateral groove 

of medulla. 



Ventricular floor. 



Ventricular floor. 



Accessory root. . ] 



Spinal root. 



( Dorso - lateral 



■ Closed medulla. 



groove of medulla ) 

Lateral column of "] flntermedio - lateral 
y *{ column of cells in 
spinal cord. cord. 



12th, Hypoglossal. . 



\ 



Ventro 



lateral 



groove of medulla. 



Ventricular floor. 



94 The Brain and Spinal Cord. 

The posterior ten cranial nerves arise from two series of nu- 
clei, — (i) a ventral or anterior and (2) a dorsal or posterior series 
The ventral series corresponds to the anterior cornu of gray mat- 
ter in the spinal cord. It is entirely motor or efferent. The dor- 
sal series is regarded as the continuation ot the posterior cornu 
and is sensory or afferent in function. Each series is composed of 
a double chain of nuclei: (a) a mesial chain, derived from the 
base of the cornu and (b) a lateral chain, from the caput cornu. 

(i). VENTRAL SERIES. 

(a) The mesial chain is close to the mesial line, beneath the 
funiculus teres and aqueduct of Sylvius. It gives origin to the 
Hypoglossal (12th), Abducent (6th), Pathetic (4th) and Oculomo- 
tor (3d) nerves; also to accessory motor roots of the 10th and 9th 
nerves in the nucleus teres; and to the 5th in the floor of the 
Lylvian aqueduct. All are efferent or motor. 

(b) Lateral chain— This also is motor. It lies external to the 
mesial chain, beneath the internal parts of the locus cceruleus 
and trigonum vagi. Converging slightly toward its fellow of the 
opposite side it extends backward into the closed medulla. It is 
regarded as the head of the anterior cornu. From the lateral 
chain of the ventral series arise, — the accessory root of the Spinal 
accessory (nth), posterior to the 4th ventricle; the chief motor 
roots of the Pneumogastric (10th) and Glossopharyngeal (9th); 
the root of the Facial (7th); and the principal motor root of the 
Trifacial (5th); also an accessory motor root of the 10th and 9th 
nerves, from the nucleus ambiguus. 

(2) dorsal series 

(a) Mesial chain of nuclei— It corresponds to the base of the 
posterior gray cornu. Placed external to the ventral series, it is 
covered by the lateral part of the trigonum vagi, the acaustic tri- 
gone and superior peduncle of the cerebellum. It is entirely sen- 
sory or afferent, and it contains the principal sensory nuclei of 
the Pneumogastric (loth), and Glossopharyngeal (9th); the dorsal 
nucleus of the Auditory (8th); and the main sensory nucleus of the 
Trifacial (5th). 

(b) The lateral chain of the dorsal series is most external in 
position. It is located beneath the tubercle of Rolando and the 
restiform body. In it are contained the accessory sensory nucleus 



After-Brain. 95 

of the trifacial (5th) called the nucleus of Rolando; and the ven- 
tral (accessory) and lateral nuclei of the eighth or auditory nerve. 
These nuclei are sensory or afferent. 

The Olfactory ( 1 st)and the Optic(2d)nervesare sensory or afferent 
and probably belong to the dorsal nerves, but this is difficult of de 
monstration. 



THE SPINAL CORD. 



The spinal cord is developed from the posterior part of the 
neural tube, and forms the corresponding portion of the central 
axis of the nervous system. 

Extent— It is continuous with the medulla oblongata, above; 
an€l, in the adult, reaches to the lower border of the first lumbar 
vertebra. Its length is 17 inches or 18 inches. In a very slender 
process, the filum terminate, the cord is continued beyond the first 
lumbar vertebra. That process and the lower spinal nerves form 
the cauda equina, which is inclosed in a sheath composed of the 
arachnoid and dura mater. The filum terminale, for some dis- 
tance, contains a prolongation of the central gray matter and ven- 
tricle of the cord; and, also, a few fibers, which suggest the cocy- 
geal nerves of lower animals. The filum terminale pierces the 
arachno-dural sheath opposite the second sacral vertebra; and 
thence, the three meninges are continued in a fibrous process, 
called the central ligament of the spinal cord. The central liga- 
ment is inserted into the back of the coccyx. 

In the foetus before the third month, the cord and spinal canal 
are of equal length. At birth the cord reaches the third lumbar 
vertebra, and it continues to recede with the rapid growth of the 
vertebra to adult life. 

Size — The spinal cord is shaped like a cylinder, slightly flat- 
tened from before backward (dorso-ventrally). Its longest diame- 
ter is transverse and measures less than half an inch, except in 
the cervical and lumbar enlargements ol the cord. In the latter, 
it equals a half inch; and, in the former, it slightly exceeds it. 
The thoracic portion of the cord is small and nearly cylindrical in 
shape. 

The cervical enlargement extends from the medulla oblongata 
to the second thoracic vertebra. Its greatest diameter is on a 
level with the fifth intervertebral disk. It gives origin to the 
nerves which form the cervical and brachial plexuses. 

96 



The Spinal Cord. 97 

The lumbar enlargement begins at the tenth thoracic vertebra 
and increases to the twelfth. Opposite the first lumbar vertebra, 
it tapers off almost to a point, the conus terminalis, but a very 
small process continues in the filum terminale. From the lumbar 
enlargement arise the nerves forming the lumbar and sacral plex- 
uses. 

The spinal cord is closely invested by pia mater, whose trabe- 
cular form the connective tissue frame-work of the cord and 
transmit blood vessels into it. It is less closely invested by the 
arachnoid. The subarachnoid spaces and the medulli-spinal 
veins intervene. Still more loosely does the dura mater invest 
the cord. On either side, a vertical sheet of pia mater, notched 
externally and called the ligamentum denticulatum, attaches the 
cord to the dura. Surrounded by its meninges and the interven- 
ing spaces, the cord is much smaller than the spinal canal. The 
dura is separated from the walls of the spinal canal by the 
meningo-rachidian veins, areolar tissue and fat. Divested of 
meninges and nerves, the spinal cord weighs about one ounce 
and a half avoirdupois. 

Sixth ventricle— The central canal of the spinal cord is the rep- 
resentative of the cavity of the neural tube. It is just visible to 
the naked eye; but it extends throughout the cord and expands 
above into the fourth ventricle. In the filum terminale, it is also 
dilated. It is lined with columnar ciliated cells which stand on a 
thick lamina of substantia gelatinosa Rolandi. 

SURFACE. 

Fissures of the spinal cord— The spinal cord is incompletely 
divided into symmetrical lateral halves by the anterior and the 
posterior median fissure. 

The anterior median fissure is the broader and shallower of 
the two. It extends from the posterior end of the ventral surface 
of the pons (foramen caecum of Vicq d'Azyr) down the anterior 
median line of the medulla and cord. Its floor is formed by the 
anterior \ or white, commissure. Both layers of pia mater dip down 
into it and inclose the anterior spinal artery and its branches. The 
anterior median fissure is interrupted at the junction of the cord 
and medulla by the decussation of the pyramids. Below the lum- 
bar enlargement it gradually disappears. 

The posterior median fissure is narrow and deep. It ex- 



98 The Brain and Spinal Cord. 

tends down the posterior median line of the cord from the middle 
of the dorsal surface of the medulla. It divides the cord dorso- 
ventrally beyond its middle. The floor of the fissure is formed 
by the posterior, or gray, commissure, which, with the white com- 
missure, separates the posterior from the anterior median fissure. 
The posterior median fissure is occupied by a lamina of connect- 
ive tissue from the deep layer of the pia mater, the posterior 
septum. In the posterior septum ramify branches of the two pos- 
terior spinal arteries and tributaries of the medulli-spinal veins. 

Posterolateral fissure — Each lateral half of the spinal cord 
is partially divided, near the junction of the posterior fourth with 
the anterior three-fourths of its semicircumference,by the postero- 
lateral fissure. The fissure is situated opposite the posterior 
cornu of gray matter, to which it transmits the posterior roots of 
the spinal nerves. It is continuous above with the dorso lateral 
groove of the medulla. It separates the posterior surface and the 
antero lateral surface from each other. 

Anterolateral fissure— It is convenient to regard the narrow 
longitudinal area, through which issue the anterior roots of the 
spinal nerves, as the antero-lateral fissure. The anterior roots do 
not emerge in line one above another, nor is there any groove on 
the surface of the cord, so the fissure can not be exactly located. 
It is situated opposite the anterior cornu of gray matter and in 
line with the ventro-lateral groove of the medulla oblongata. It 
subdivides the antero-lateral surface into anterior and lateral 
surfaces. 

The posterior intermediate furrow is a slight longitudinal 
groove which subdivides the posterior surface into postero-median 
surface and postero-lateral surface. From it a connective tissue 
septum extends into the cord and separates the columns of Goll 
and Burdach from each other. The posterior intermediate furrow 
is found only in the upper part of the cord, in the cervical and 
dorsal regions. 

INTERIOR. • 

Columns of the cord— The spinal cord is divided into three 
great columns which correspond to the three great surfaces, 
namely: the anterior column, lateral column and posterior 

column. The anterior and lateral columns are separated from 
each other by the anterior cornu of gray matter and the anterior 



The Spinal Cord. 99 

roots of the spinal nerves. Together they constitute the antero- 
lateral column. The lateral column stands between the anterior 
and posterior cornua of gray matter. It is inclosed by the ante- 
rior and posterior roots of the spinal nerves. It is separated from 
the posterior column by the posterior gray cornu and the postero- 
lateral fissure. The anterior and posterior columns bound the 
corresponding median fissure. 

The spinal cord is composed of — I. Gray matter, in the cen- 
tral part; and II. White matter, in the peripheral area. It is like 
the medulla and pons in having the white matter on the surface. 
The substance of the cord is largely made up of medullated nerve 
fibers which form the white columns. In the gray matter, there 
are multipolar nerve cells of both the large vesicular and small, 
round varieties. Nerve fibers and cells are all imbedded in neu- 
roglia and supported by connective tissue trabecule from the pia 
mater. 

I. GRAY MATTER OF THE CORD. 

A column of gray matter, crescentic in section, extends through 
the center of each lateral half of the spinal cord. The crescent 
is convex mesially; and is joined to its fellow, a little in front of 
the middle, by a transverse lamina of gray matter, called the pos- 
terior commissure. The points of the crescent are directed for- 
ward and backward, respectively, and form the anterior and pos- 
terior cornua. Together, the two crescents and the posterior 
commissure form an H-shaped column of gray matter. The 
H-shaped column is well marked in the cervical and thoracic re- 
gions; but, toward the lower end of the cord, the crescents be- 
come short and thick and the gray column is almost cylindrical. 

The gray matter of the spinal cord is of two kinds: (1) The 
substantia gelatinosa Rolandi, which forms (a) a thin layer be- 
neath the pia mater; (b) a cap for the head of the posterior cornu 
and (c) an envelope for the central canal, or ventricle, of the 
cord. (2) The substantia spongiosa. The latter forms the 
greater part of the H-shaped column. Imbedded in neuroglia is 
a network of medullated nerve fibers running longitudinally, dor- 
so-ventrally and transversely, which gives it a spongy appearance. 

Gray crescent — It is made up of (1) the anterior cornu; (2) 
the center, which is joined to its fellow of the opposite side by 
the gray commissure; and, (3) the posterior cornu. Sometimes 



ioo The Brain and Spinal Cord. 

there is a lateral projection from the center of the crescent in the 
cervical and upper dorsal region, called the lateral horn. 

(i) The anterior cornu is short and thick compared with the 
posterior cornu. It is thickest in the cervical and lumbar enlarge- 
ments; in the mid-thoracic region it is more slender. It does not 
reach the surface of the cord as does the posterior cornu. It ends 
in a bulbous, serrated head, which points toward the exits of the 
anterior roots of the spinal nerves. Together with the anterior 
root-fibers, it separates the anterior and lateral columns of the 
cord. Cells. — The anterior cornu contains two columns of large 
vesicular cells, a mesial and a lateral column. Each column 
may be further divided into a ventral and a dorsal part, The 
mesial and lateral columns are constant throughout the cord. 
The axons of their cells form the greater part of each anterior 
spinal root. From the lateral column and from part of the 
mesial, the axons enter the spinal nerves of the same side; the 
remainder pass through the anterior (white) commissure to the 
opposite nerves. They are distributed to the muscles of the 
trunk and extremities. The end-tufts of the direct and crossed 
pyramidal fibers are in relation with these cells of the anterior 
cornu. So do some collaterals of the posterior roots of the spinal 
nerves end in relation with them. 

(2) The central part of the crescent contains three columns 
of cells: The iniermedio-lateral column of large vesicular cells, 
situated near the lateral surface of the crescent; the middle col- 
umn (Waldeyer), deep in the crescent at the junction of the gray 
commissure; and the vesicular column of Clark, which is situated 
near the inner surface of the base of the posterior cornu. 

The intermedio=lateraI column is best marked in the thoracic 
region; but is found also in the cervical and lumbar cord. Its cells, 
which are large and vesicular, are in relation with end-tufts of col- 
laterals from the posterior roots; and they give rise to efferent fi- 
bers that enter the anterior roots of the spinal nerves. The latter 
probably supply the muscles of the glandular and circulatory sys- 
tems (Morris). 

The middle column (Waldeyer) is composed of moderate-sized 
cells, which are most abundant in the cervical region where the 
column is best shown. Collaterals from the posterior spinal roots 
have been traced among the cells, and possibly the cells give rise 
to some of the fibers of the antero-lateral ascending cerebellar 



The Spinal Cord. ioi 

tract; but nothing is certainly known of the function of the 
column. 

Clark's column is limited to the thoracic region; but it is rep- 
resented by the nuclei of Stilling in the lumbar region and in the 
medulla oblongata by the accessory cuneate nucleus. Clark's 
cells are in relation with the end-tufts of posterior-root collaterals 
(paraxons); and, perhaps, of certain axons, also from the posterior 
roots of the spinal nerves. The axons of Clark's cells form the 
direct cerebellar tract, the antero-lateral ascending cerebellar 
tract and help to form the anterior roots of the spinal nerves. The 
last are distributed as "inhibitory nerves to the blood-vessels, 
glands, and to the walls of the alimentary canal." (Morris). 

(3) The posterior cornu, except in the lumbar cord, is slen- 
der. It is longer than the anterior cornu and reaches the surface 
in the postero-lateral fissure, where it receives the posterior roots 
of the spinal nerves. The posterior cornu presents a slight 
enlargement near its extremity, called the caput cornu, which 
tapers off to the apex cornu and is joined to the base of the horn 
by a constricted part, the cervix. The head of the posterior 
horn is capped by the substantia cinerea gelatinosa of Ro- 
lando. The posterior cornu separates the posterior from the 
lateral column of the cord. 

The cells of the posterior cornu are very numerous. They 
are smaller than the cells of the anterior cornu and less defi- 
nitely grouped. They are classified as follows: (a) the periphe- 
ral cells with one long process, the comet cells (Waldeyer); (b) 
central cells; (c) basal cells; (d) cells of the substantia gelati- 
nosa, which are small and round (Gierke and H. Virchow);and 
(e) the solitary, fusiform cells, scattered throughout the poste- 
rior horn. The dendritic processes of these cells probably ramify 
in the gray matter adjacent to them. The axons run in various 
directions and their destination is unknown. Some of them run 
forward into the anterior commissure and anterior cornu, and 
are believed to be the small fibers in the anterior roots of the 
spinal nerves; other axons have been traced into the spinal 
nerves through the posterior roots (Freud and others). Many 
posterior-root collaterals terminate in ramifications about these 
cells. The axons forming the lateral group of small fibers in 
the posterior roots of the spinal nerves, end about the small 
round cells in the substantia gelatinosa Rolandi. 



102 The Brain and Spinal Cord. 

The posterior, or gray, commissure completes the gray mat- 
ter of the cord. It unites the two gray crescents together a little 
in front of their center, except in the lumbar region where it joins 
their centers. It forms the floor of the posterior median fissure; 
and, in front, is in relation with the white commissure. It is 
pierced longitudinally by the central canal of the spinal cord, 
around which is a thick envelope of substantia gelatinosa. The 
posterior commissure is composed of neuroglia in which are im- 
bedded nerve cells and medullated nerve fibers. The medullated 
fibers are chiefly collaterals which course from the posterior nerve- 
roots through the commissure to the gray crescent of the opposite 
side. 

II. WHITE MATTER OF THE CORD. 

The white matter of the spinal cord is disposed in its peripheral 
area and in the anterior commissure. It is composed of mudul- 
lated nerve fibers (axons and paraxons) imbedded in a small 
amount of neuroglia; and, like the gray matter, it is richly supplied 
with blood vessels. It is also supported by a connective tissue 
network derived from the pia mater. The fibers run transversely, 
dor so-ventr ally and longitudinally. 

Transverse fibers are found running between tbe longitudinal 
columns and the gray matter, or vice versa, and are continuous 
with the longitudinal fibers. A quite definite lamina of transverse 
fibers forms the anterior commissure. 

The anterior, or white commissure— It connects the ante- 
rior (white) columns of the cord with the opposite gray crescent. 
It is located in front of the gray commissure, and forms the floor 
of the anterior median fissure. It is composed of medullated 
fibers belonging to the direct pyramidal tract and the antero- lat- 
eral ground bundle, and of the crossed fibers to the anterior roots 
of the spinal nerves. 

The dorso=ventraI fibers are those of the anterior roots of the 
spinal nerves, in their course from the gray matter to the surface 
of the cord. 

The longitudinal fibers comprise most of the white matter in 
the cord. They are disposed around the gray crescent in ten 
bundles or tracts. The tracts are not visible to the naked eye, nor 
under the microscope in a healthy adult cord; they have been 
located by embryological and pathological investigations. The 



The Spinal Cord. 103 

longitudinal fibers arise in the brain or in spinal ganglia and de- 
scend 'in the cord; or they arise in the spinal cord or ganglia and 
ascend in the cord toward the brain. Thus the tracts are charac- 
terized as ascending and descending tracts: 

Ascending tracts: (1) Antero-lateral ascending cerebellar 
tract, (2) Direct cerebellar tract, (3) Postero-lateral tract, (4) 
Postero-median tract, and (5) Marginal tract of Lissauer. 

Descending tracts: (1) Direct pyramidal tract, (2) Crossed 
pyramidal tract, (3) Antero-lateral descending cerebellar tract, 
and (4) Comma tract. 

Mixed, ascending and descending tract — The Antero-lateral 
ground bundle. 

The tracts of the antero-lateral column of the spinal cord 
are seven in number, viz., the antero-lateral ground bundle, two 
pyramidal tracts, three cerebellar tracts and the marginal bundle 
of Lissauer. 

The antero-lateral ground bundle occupies the deep part of 
the column. It embraces the anterior cornu of gray matter and 
the outer surface of the base of the posterior cornu. It approaches, 
but does not quite reach the surface of the cord. It is separated 
from the anterior median fissure by the direct pyramidal tract; 
the antero-lateral descending and ascending cerebellar tracts run 
between it and the surface of the cord; and, behind, it is in rela- 
tion with the crossed pyramidal tract. The antero-lateral ground 
bundle is composed of ascending and descending fibers which are 
commissural. The fibers connect different segments of the 
cord, and are in part continued upward into the fillet and poste- 
rior longitudinal bundle. 

The direct pyramidal tract (Tlirck's column) occupies a thin 
area next the anterior median fissure. It is the continuation of the 
same tract in the medulla. Its fibers are axons of cortical cells 
in the Rolandic region of the cerebrum. As the tract descends, 
the fibers decussate through the anterior commissure, and termi- 
nate in relation with the cells of the opposite anterior cornu. 

The antero= lateral descending cerebellar tract (Loewenthal's 
column) together with the ascending antero-lateral cerebellar tract, 
occupies a thin peripheral area, broadest posteriorly, which 
extends from the direct pyramidal tract outward and backward 
over the antero-lateral ground bundle, to the middle of the lat- 
eral surface of the cord. Its posterior border is in relation with 



104 The Brain and Spinal Cord. 

the direct cerebellar tract and the crossed pyramidal tract. The 
fibers of the two tracts are mingled together; but the descending 
fibers are found, chiefly, in the anterior part of the common area 
and the ascending in the posterior part. The descending fibers 
are axons from the cortical cells of the cerebellum. They 
descend to the spinal cord through the inferior and middle cere- 
bellar peduncles and the lateral area of the medulla. Some of 
them pass directly into the anterior roots of the spinal nerves. 

A ntero= lateral ascending cerebellar tract (column of 
Gowers)— It is found chiefly in the posterior part of the area com- 
mon to it and the descending tract. It is composed of axonic 
processes of Clark's vesicular cells. It ascends through the 
lateral area of the medulla and the superior cerebellar peduncle 
to the worm of the cerebellum. Most of its fibers terminate in 
the worm; a few join the lower fillet and end in the posterior 
quadrigeminal body. 

The direct cerebellar tract (dorso-lateral cerebellar tract) 
runs posterior to the antero-lateral tracts. It is superficially lo- 
cated, and extends from the middle of the lateral surface of the 
cord back to the postero-lateral fissure, except in the lumbar cord. 
There, its absence allows the crossed pyramidal tract to come to 
the surface. The direct cerebellar tract terminates in the worm 
of the cerebellum. In the medulla, it forms a part of the restiform 
body. Its fibers are axons from Clark's vesicular cells. 

The crossed pyramidal tract forms a considerable part of the 
lateral column of the spinal cord. It is covered, superficially, by 
the cerebellar tracts in the cervical and dorsal cord; but in the 
lumbar cord, it forms part of the surface. Its deep surface is in 
relation with the antero-lateral ground bundle and marginal bun- 
dle of Lissauer. The fibers composing it are axons of cells in the 
Rolandic region of the cerebral cortex. They arise with those of 
the direct pyramidal tract; and they run as one tract down through 
the genu of the internal capsule, the middle third of the crusta, 
the ventral longitudinal fibers of the pons and the pyramid of the 
medulla. In the medulla the two tracts separate. The crossed 
tract decussates with its fellow throngh the anterior median fissure, 
pierces the anterior gray cornu and descends in the cord. It ter- 
minates in relation with the cells of the anterior cornu. The pyra- 
midal tracts are the cerebral motor tracts. 

The marginal tract of Lissauer is a small tract composed of 



The Spinal Cord. 105 

the outer set of small fibers in the posterior roots of the spinal 
nerves. It is situated on the lateral surface and apex of the caput 
cornu. Its fibers are axons of the spinal ganglia on the posterior 
roots of the nerves; after ascending a short distance they end 
about the cells of the substantia gelatinosa Rolandi. 

Tracts of the posterior column of the cord— There are three 
tracts in this column, viz., the postero-lateral, the postero-median 
and the comma tract. 

Postero-lateral tract (Burdach's column) — It runs upward 
just mesial to the posterior cornu of gray matter. It is made up 
of ascending branches of the posterior roots of the spinal nerves. 
It becomes the funiculus cuneatus in the medulla; and it ends in 
the nucleus cuneatus. Some of the fibers end in the gray matter 
of the cord as they ascend. In the midst of the postero-lateral 
tract is a small bundle of descending fibers — 

The comma tract — It is comma-shaped in section. It is be- 
lieved to be composed of descending branches of the posterior 
roots of the spinal nerv&s. It is considerably intermingled with 
fibers of the postero-lateral tract, and its termination is uncertain. 

The postero= median tract (Goll's column) ascends between 
the postero-lateral tract and the posterior median fissure. Like 
the postero-lateral tract, it extends in depth ventrally to the gray 
commissure. It is composed of ascending branches of the poste- 
rior roots of the spinal nerves. Continued into the medulla ob- 
longata, the postero-median tract becomes the funiculus gracilis. 
It terminates at the clava, the fibers ending in relation with the 
cells of the nucleus gracilis. A number of fibers, diverging from 
the tract, end in the gray matter of the spinal cord. 

ROOTS OF THE SPINAL NERVES. 

There are thirty-one pairs of spinal nerves which arise from 
the side of the cord. Each nerve has two roots: an anterior, ef- 
ferent or motor root, and a posterior, afferent or sensory root. 
These roots descend more or less from their origin to the inter- 
vertebral foraman in which they unite to form the spinal nerve. 
The roots of the first cervical nerve are horizontal; those of the 
first dorsal nerve descend the width of a vertebra and those of 
the twelfth dorsal, the width of two vertebrae; while the roots of 
the coccygeal nerve extend from the first lumbar vertebra to the 
second piece of the coccyx. 



106 The Brain and Spinal Cord. 

Anterior root — In all spinal nerves, except the first, the an- 
terior root is smaller than the posterior. It is composed of from 
four to six funiculi, which soon combine into two bundles. After 
piercing the dura mater, the anterior root unites with the poste- 
rior, beyond the latter's ganglion, and forms a spinal nerve. 

Superficial origin — The anterior root is composed of medul- 
lated axons which issue from t^e narrow longitudinal area com- 
monly called the antero-lateral fissure. 

Beep origin — The medullated axons arise (i) from the corti- 
cal cells of the cerebellum; and (2) from the H-shaped column of 
the spinal cord, as follows: from the mesial, lateral, and interme- 
dio-lateral columns of cells and the posterior cornu of the same 
side; and from the mesial column of cells and posterior cornu of 
the opposite side. The small fibers of the anterior roots are be- 
lieved to be from the posterior cornua. 

The posterior root is the sensory or afferent root. It is larger 
than the anterior root, except in the case of the first cervical nerve; 
and is composed of from six to eight funiculi, which also combine 
at once into two bundles. The posterior root pierces the dura 
mater, separately. It unites with the anterior root in the inter- 
vertebral foramen. Near the outer end, it presents a swelling 
which contains gray matter and nerve cells, and is called a spinal 
ganglion. (It is occasionally absent on the first nerve.) The 
posterior root, external to the ganglion,is made up of the dendritic 
processes of the ganglion cells. These dendrites extend to the 
most distant parts of the body; they are the sensory fibers of the 
spinal nerves. Internal to the ganglion, the posterior root is 
composed of axons, which arise from the ganglion cells. Both 
the axonic and dendritic processes are medullated. 

Superficial origin — The posterior roots of the spinal nerves 
enter the posterior fissure; and, at once, divide into an outer set 
of small fibers and an inner set of large fibers with some small 
ones interspersed. 

Deep origin — 1 he outer set of small fibers ascend a short dis- 
tance, along the external surface of the caput cornu; and end in 
ramifications about the cells of the substantia gelatinosa Rolandi. 
They form the tract of Lissauer. Of the inner set of fibers from 
the posterior root, probably a few (the small fibers) run directly 
to Clark's column, and terminate about its cells. It is possible 
that all these small fibers of the posterior roots are collaterals 



The Spinal Cord. 107 

(paraxons) originating near the spinal ganglion. All the large 
fibers of the inner set, upon entering the cord, divide, T-like, into 
ascending and descending branches; and the main fiber, with each 
of its T-branches, gives off many collaterals. The collateral 
branches or paraxons, terminate about the cells in the posterior 
cornu, center and anterior cornu of the gray crescent on the same 
side; and, some of them, run through the gray commissure to the 
opposite crescent. The ascending T=branches form the poste- 
ro-lateral and postero-median tracts of the cord. They end for 
the most part in the nucleus cuneatus and nucleus gracilis of the 
medulla; a few of them terminate in the cord. The descending 
T=branches, except a small bundle of them, run down in the 
posterior cornu of gray matter. They are thought to end in the 
gray matter of the lower segments of the cord. One small 
bundle of the descending T-branches descends within the 
postero-lateral tract as the comma tract. 



END. 



INDEX. 



Arteries \ Veins, Sinuses and Choroid plexuses are not repeated, 
but are found under their respective initials. 



Abducens nerve, origin 39, 79, 91, 93 

Acaustic striae 91 

Acervulus cerebri 30 

Afferent or sensory nerves — 94, 105, 

106 

processes 44, 45 

After-brain 53, 78, 95 

Ala cinerea 92 

Alae of cerebellum 65 

Alveus " 48 

Amygdalae of cerebellum 67, 68 

of cerebrum 24, 26 

Annectant convolutions 9,10 

Ansa lenticularis 34,41 

peduncularis 34 

Anterior crescentic lobule 65 

Anterior commissure... 16, 28, 31, 50, 

56 

choroid tela 30 

Anterior perforated lamina or space 

15, 55 

Aqueduct of Sylvius 27-29, 39, 49, 

53,58 

Arachnoid 4, 52, 96 

Arbor vitae 62, 65, 71 

Area of Broca 15, 55 

of cerebral softening 60 

Areas of medulla 83-88 

Arteries, choroid 60 

end 60 

of cerebellum 72 

of cerebrum 58, 59 

circle of Willis 58 

corticle 58 

ganglionar 59 

of pons 72 



of spinal cord 97, 98 

Ascending root of fifth nerve. . . . 76, 88 

tracts of cord 103 

Association fibers of cerebellum 72 

of cerebrum 50. 51 

Auditory lobes 43 

nerve, origin. 79, 83, 88,92-95 

nuclei, dorsal 92 

lateral 88 

ventral (or accessory). 41, 88 

Axis- cylinder 44, 45 

Axon 44,45, 106 

B 

Base of brain 12 

Blood supply of cerebellum 72 

of cerebrum and mid-brain. .. 

58-61 

cortical system 58, 59 

ganglionic system 59-61 

of pons 77 

of spinal cord 97, 98 

Brachium, anterior 42 

posterior 42 

Brain, development 51 

grand divisions 7 

membranes 3 

sand 30 

vesicles, primary 52, 53 

secondary 52-58 

derivatives 53-58 

Broca's area 15, 55 

Bulb, olfactory 15,55 

spinal. 78 

Bundle of Solly 87 

of Vicq d r Azyr 13, 21, 33 

Burdach's column 105 



109 



no 



Index. 



c 

Calamus scriptorius 88 

Calcar avis(hippocampus minor)25,54 

Calcarine fissure 11 

Calloso-marginal fissvire 10 

Caput cornu posterioris 99, 101 

Cauda equina 96 

Caudate nucleus 17, 22, 24, 54 

Cells of cerebellar cortex 69, 70 

cerebellar ganglia 70, 71 

cerebral coi tex 44 

cerebral ganglia 44 

corpora quadrigemina 43 

corpora geniculata 34 

corpus dentatum 70 

olivary nucleus of medulla 70, 89 

of pons ,77 

spinal cord 100, 101 

anterior cornu 100 

posterior cornu 101 

substantia nigra 38 

Central canal of spinal cord . . .97, 102 

Central fissure 8 

Central lobe 10 

lobule 65 

Centers of hearing 10 

of smell 10 

of taste 10 

Cerebellum 62-73 

Cerebro-spinal axis 96 

fluid 5,28 

Cerebrum 8-35 

blood supply 58-61 

cavity or ventricle 16-27 

development 51-58 

fissures and lobes 8-16 

gray matter 43-49 

white matter 49-51 

Chiasma, optic 12, 13 

Choroid plexus of lateral ventricle. 22, 

. 25, 26,28, 31 

of fourth ventricle 81, 91 

of third ventricle 30, 57 

veins 25 

Choroid tela, anterior 5, 30, 31 

posterior 5,81 

Cingulum 50 

Circle of Willis 58 

Clark's column 101 



Claustral formation 47 

Claustrum 48 

Clava 87,89 

Clivus 65, 66 

Collateral fissure — 11 

Column of Burdach 105 

of Goll 105 

Columns of cells in spinal cord. .. 100, 

101 

Commissures of brain, anterior.. ..28, 

31, 50,56 

middle 28,57 

posterior 28, 29, 57 

of Gudden 14, 35 

optic 12,13,29, 57 

of spinal cord 97, 98, 102 

Commissural fibers of cerebellum. . . 72 

of cerebrum 50 

Conarium 30,57 

Conjugate deviation 40 

Conus terminalis 97 

Convolutions of cerebrum 9-16 

of base. . . / 12-16 

of convex surface 9-1 1 

of mesial surface 11, 12 

Cornu Ammonis 26, 48, 54 

Cornua of lateral ventricle 25-27 

of spinal cord 99-101 

Corona radiata 50 

Corpora albicantia.. 12, 13, 21. 29, 57 

geniculata 32, 34 

quadrigemina. .37, 42, 43, 58 
Corpus callosum 14, 16, 18, 19, 50, 56 

body 19,25 

genu 19, 25 

peduncles ! ... 19 

rostrum 19,25 

splenium 19 

Corpus dentatum 70 

fimbriatum .....20,26,27,51 

striatum 17, 22-24,54,55 

subthalmicum 39 

Cortex, cerebellar 69, 70 

cerebral 46-48 

Cranial nerves, origin 92-95 

Crus cerebri, or crura 37 

Crusta 13, 37, 50, 58 

Culmen 65 

Cuneate lobe .'. .11 



Index. 



hi 



Cuneate tubercle. 



Decussation of fillets 83, 89 

of optic nerves 12,13, 29 

of pyramids 78 

Dendrites 44, 45, 106, 107 

Dentate body and nucleus 70 

fissure 70 

Denticulate ligament 6. 97 

Descending tracts of cord 103 

Development of brain 51 

of spinal cord 52, 96 

Diaphragm sellae 13 

Digastric lobule 67, 68 

Direct sensory tract 38 

Dura mater of brain .3 

of cord 4, 96 



Efferent nerves, cerebral 94 

spinal 105, 106 

Efferent processes 44, 45 

Eighth nerve 79, 83, 88, 92-95 

Eleventh nerve 79, 83, 93, 94 

Eminentia acaustica 92 

cinerea 91, 92 

collateral 26,27, 54 

teres 88, 91 

End-arteries 60 

End-tufts or end-brushes 45 

Epencephalon 53, 58, 73 

Ependyma 22, 28, 90 

External arciform fibers 80 

External capsule 24 

External geniculate body 32, 34 



Facial nerve, origin.. ..79, 88, 91, I 



94 

Falx cerebelli and cerebri 3 

Fascia dentata 12, 26, 27 

Fasciculus or funiculus, cuneatus..81 

86, 87 

gracilis 81,86,87 

longitudinal, inferior 51 

posterior 40, 76 

superior 51 

olivary 42 



Rolando 81, 86, 87 

perpendicular 51 

solitarius 88 

teres 76, 88 

uncinate 51 

Fibers, arciform -80, 83 

axons 44, 106 

axidendrons 45 

collaterals or paraxons.45, 107 

dendrites 44, 45, .106, 107 

of cerebellum ..71, 72 

of cerebrum 49-51 

of medulla 83-88 

of mid-brain.. .49-51 

of pons 74-77 

of spinal cord 102-107 

Fifth nerve, origin.. 49, 74, 88, 91, 93 

94 

ventricle 20, 21,56 

Fillet ..38, 40, 41, 76, 85 

of gyrus iornicatus 50 

origin 40 

Filum terminale 6, 96 

First nerves, origin 15, 92, 95 

Fissura prima 15. 16, 55 

Fissural ventricle 21 

Fissures of cerebellum — 64-67 

great horizontal 64 

of upper surface 64. 65 

of lower surface 66 

Fissures of cerebrum 8-16 

great long:tudinal 8, 12 

great transverse — 8,26,55 
of Bichat (or transverse) .. .8 

of base 14 

of convex surface 8 

mesial surface 10 

Fissures of medulla 78, 79 

of spinal cord 78,97,98 

Flexures of neural tube 52 

cervical 52 

mesencephalic 52 

metencephalic 52 

Flocculus 67 

Floor of fourth ventricle 91, 92 

Folium cacuminis 65, 66 

Foramen caecum of Vicq d' Azyr..77, 

97 

of Majendie 4,81,90 



I 12 



Index. 



of Monro... .22, 28, 29, 32, 

54 

Foramina of Key and Retzius...4, 81, 

, 90 

Forceps, major 19, 25 

minor 19. 25 

Fore-brain 53 

Formatio reticularis of medulla 82, 

84,85 

of pons 76 

Fornix, body.... 20, 22, 25, 23,50, 56 

anterior pillar 20, 32 

posterior pillar. . . . .20, 26, 27 

development 55, 56 

Fourth nerve, origin 13, 39, 40, 71, 

74 

Fourth ventricle.... 53, 58,62, 79,82, 

90-92 

Fovea, inferior ..91, 92 

superior 91 

Fraenulum of cerebellum 65 

of valve of Vieussens . . .74 

Frontal lobe 9,14 

Funiculus or fasciculus (see) 

Furrow, posterior intermediate 98 

Fusions .55, 56 

G 

Galen, veins of 3, 25, 60 

Ganglia, cerebellar 70, 71 

cerebral 48, 49 

spinal 106 

Geniculate bodies .. .32, 34 

General cavity of cerebrum 16 

boundaries 19,20 

divisions 20 

Genu of corpus callosum 19, 25 

internal capsule 17 

Glands of Pacchioni 4 

Globus pallidus 23 

Glossopharyngeal nerve, origin 79,83, 

92, 93, 94 

Golgrs types of cells 45 

Goll's column 103, 105 

Gower's tract 104 

Grand division of brain 7 

Gray and white matter of cerebrum 

and mid-brain 43-51 

Gray matter of cerebellum 69-71 



of cerebrum... 44, 46-49 

of medulla 88 

of mid-brain 38, 39, 40, 

42, 43 

of pons 77 

of spinal cord.. ..99-102 

Great horizontal fissure 64 

Groove basilar 73, 75 

dorso-lateral 79 

ventro-lateral 79 

Gudden's commissure 14, 35 

Gyrus fornicatus 11, 12 

fillet of 50 

Gyri operti 10, 55 

H 

Habenulae 30 

nucleus of 33 

trigone of 32 

Hemispheres of cerebellum 62 

of cerebrum 53-57 

cortex 46-48 

white matter 49-51 

Hemisphere vesicle 54 

thickenings — 55 

Hind-brain 53, 62-77 

Hippocampal convolution 11, 12 

fissure 11 

Hippocampus major 26,48,54 

minor 25, 54 

H-shaped column 99 

Hypoglossal nerve, origin.. 79, 83, 91- 

93,94 

Hypophysis or pituitary body.. 12, 13 

I 

Incisura cerebelli (notch) 62 

anterior 62 

posterior 62 

Inferior peduncles of cerebellum. 63, 72 
Inferior surface of cerebellum.. .66-69 

of cerebrum 12 

Infundibulum 12,13,29, 57 

Inter-brain 27-35, 57 

Interlobular fissures 64 

lower surface of cere- 
bellum 66,67 

upper surface of cere- 
bellum 64, 65 



Index. 



ii3 



Internal capsule 16, 50. 56 

lamina, inferior 17, 26 

superior 17, 26 

genu 17 

segments 17 

Interna] geniculate body.... 32, 34, 43 

Involuted medullary lamina 48 

Island of Reil 8, 10, 14, 54 

Isthmus 11 

cerebri 36 

Iter a tertia ad quartum ventriculum 

27,28,29,39,49, 53, 58 

K 

Key and Retzius, foramina... 5, 81, 90 

L 

Lamina cinerea ,.12, 29, 49, 57 

medullary, external 33 

internal 33 

perforated, anterior 15, 55 

posterior 13, 29, 37, 38 

terminalis 12, 28, 31 

Lancisi, nerves 12 

Lateral columns of cord 98 

horn 100 

recesses 63, 71, 90 

tract of medulla 80 

ventricles 20 21-27 

body 22-25 

cornua 25-27 

Lemniscus or fillet.... .38, 40, 41, 76, 

85 

Lenticular nucleus 17 

Ligament, central 5,96 

Ligamentum denticulatum 6, 97 

Ligula 81 

Limbic fissure 11, 12 

lobe 12 

Lingula of cerebellum 65 

Lissauer's tract 104 

Lobes of cerebellum 65-69 

lower surface 67-69 

upper surface 65, 66 

Lobes of cerebrum 8-16 

of base , 12-16 

of convex surface 9,10 

of median surface 11, 12 

Lobus centralis (see Island of Reil). .. 

Lobulus centralis 65 

Locus cceruleus - . . ..91 



LoewenthaPs tract 103 

Longitudinal bundle, inferior 51 

posterior 40, 76 

superior 51 

Longitudinal fissure, great 8, 14 

Luys, nucleus of 34 

M 

Majendie, foramen of 5, 81, 90 

Marginal convolution 11 

Medulla oblongata 53, 78-95 

gray matter 88-90 

medullary or white matter 

82-88 

surface 79-82 

Medullary lamina, external 33 

internal 33 

Medullary velum, inferior. .62, 63, 71 

superior 42, 62, 63, 71 

Medullated fibers 44, 102 

Membranes of brain and cord (see 
Meninges) 

Meninges 3-6, 52 

arachnoid 4, 52 . 96 

blood vessels 5 

nerves 5 

subarachnoid fluid 5 

space 5 

tissue 4 

villi 5 

dura mater 3, 52 

arteries 4 

nerves 4 

pacchionian bodies 4 

processes 3 

sinuses 3 

of spinal cord 4, 96 

pia mater 5, 52 

bloodvessels 5 

foramina (Majendie, Key 

and Retzius) 5 

nerves 6 

of spinal cord 6, 96 

processes 5 

Mesencephalon 53, 58 

Metencephalon 53, 58, 78 

Mid-brain 7, 36-43 

gray and white matter... 43, 
49,50 



114 



Index. 



interior 37-43 

surface.... 36, 37 

Middle commissure 28, 32, 49, 57 

Mitral cells 47 

Monro, foramen of ..22, 28, 29, 32, 54 

Monticulus cerebelli 66 

Motor area 9 

nerve roots, cranial 94 

spinal 105, 106 

Motor oculi, origin 13, 39, 93 



Nerve cells (see cells) 

Nerves cranial, origin 92-95 

spinal, origin 106 

Nerve fibers (see fibers) 

Nerve terminations, axons 45 

dendrites 45 

Nerves of Lancisi 12, 18 

Neural tube 51,96 

Neurilemma 44 

Neuroblasts 52 

Neuroglia 44 

Nodulus 67 

Non-medullated fibers 44 

Notch of cerebellum, anterior 62 

posterior 3, 62 

Nuclei of nerves, in medulla. 89, 91-95 

in mid-brain 39, 40 

in pons 77 

of optic thalamus 33 

of Stilling in cerebellum. 70, 71 

in spinal cord 101 

Nuclei, dorsal series 94, 95 

ventral series 94 

Nuclei pontis 38 

of arciform fibers .... 83, 89, 90 

Nucleus ambiguus 89 

amygdalae 24, 26 

of auditory nerve 77 

accessory or ventral 41, 88 

dorsal 77, 92 

lateral 88 

caudatus 17, 22, 24, 81 

cuneatus ., 88 

accessory 89 

dentatus of cerebellum 70 

of medulla (olivary)81, 89 
gracilis 81. 89 



lenticularis 17,89 

Luys 34, 38, 39 

olivary 89 

red 42, 63 

Rolando 81 

O 

Obex 81 

Occipital lobe 9, 10, 47 

Oculomotor nerve 13, 39, 93 

Olfactory bulb 15, 47 

lobe 15, 55 

lobule, anterior 15, 55 

posterior 15, 16, 55 

nerves 15, 92, 95 

roots 15. 92 

sulcus 14 

tract : 15, 92 

trigone 15, 16, 55 

Olivary body 80, 99 

funiculus or fasciculus 42 

nucleus of medulla 81, 89 

cf pons 77 

peduncle 83, 89 

Olive 80 

Operculum 9, 55 

Optic commissure 12, 13, 29 

lobes 43 

nerves 14, 92, 95 

recess 12 

thalamus. 20,21,29,32-35,22, 

24,57 

tract 14,57,92 

external root 14, 92 

internal root 14, 92 

vesicle 57 

Orbital convolutions 14 

Orbital lobe 14 

Orders of neurons 45 

Origin of cranial nerves 92-95 

of spinal nerves 106 

P 

Pacchionian bodies 4 

Par vagrum (see tenth nerve) 

Parietal lobe 9, 4 6 

Paracentral lobule 9,11 

Parieto-occipital fissure 9, 11 

Peduncles of cerebellum — .... 62,= 63 



Index. 



US 



inferior :.63, 72 

middle 63, 72, 75 

superior 42, 63, 72, 74 

of cerebrum 37 

of corpus callosum 12 

of pineal body 30 

olivary 83 

Peduncular fibers, cerebellar. ...71, 72 

cerebral 49-51 

Perforated lamina, anterior. 15, 55, 16 

posterior..... 13, 29, 37, 38 

Pes accessorius (eminentia collate r- 

alis) 26 

hippocampi — 26 

Pia mater of brain 5 

of spinal cord 6,96 

Pillars of fornix 12, 13, 26, 27 

Pineal body 30, 57 

habenulae 30 

striae 30 

Pituitary body 12,13 

Pneumogastric nerve.. 79, 83, 92, 93, 

94 

Pons Tarini (posterior perforated la- 
mina) 13, 29, 37, 38 

Pons Varolii 73 

gray matter 77 

nuclei 38, 75, 77 

formatio reticularis 76, 77 

raphe 76 

longitudinal fibers 75 

transverse fibers 74 

Ponticulus of Arnold 80 

Posterior commissure 28, 29, 57 

longitudinal bundle.. .40, 76 
perforated lamina or space.. 

13,29,37 

crescentic lobule 65,66 

Postero-inferior lobule 67, 68, 69 

superior 65, 66 

Projection fibers, cerebellar 71, 72 

cerebral ..49, 50 

Prosencephalon .53-57 

Pulvinar 26 

Purkinje's cells 69, 70 

Putamen 23, 32 

Pyramid, cerebellar 67, 68 

of medulla 79, 80, 84 

Pyramidal cells.. 46, 47 



tracts, crossed.. .79, 80, 84 

direct 80, 84 

decussation of 78, 79 

Q 

Quadrate lobe, cerebellar 66 

cerebral 11 

Quadrigeminal bodies 37, 42, 43 

lamina 41 

R 

Rami of Sylvian fissure 8 

Raphe of corpus callosum 18 

of medulla 78,82 

of pons 76 

of tegmentum 40 

Recess, lateral 63, 71, 90 

optic 12 

Red nucleus :. ..42, 63 

Region of speech 9 

Rolandic 8 

Reil, island of 8, 10, 14, 54 

Restiform body 81, 87 

Rhomboidal sinus (fourth ventricle) 

90-92 

Rolando, fissure of 8 

funiculus of 81, 86, 87 

nucleus of 87, 89 

tubercle of 87 

Roof epithelium, fourth ventricle.. 81 

third ventricle 28, 29-31 

Roof of fourth ventricle, 90 

Roots of spinal nerves 105-107 

Rostrum 19. 25 

s 

Sagittal meridian 8 

Schwan, white substance of 46 

Second nerve, origin 14, 92, 95 

Sensory decussation .83, 89 

nerves 94, 105 

Septum lucidum.... 12, 21, 22, 25, 55 

fenestrated 5 

of medulla (raphe) 78-82 

of pons (raphe) 76 

of spinal cord 98 

Seventh nerve, origin 79,88,91,93, 

94 

Sinuses, cavernous 4 



u6 



Index. 



circular 4 

lateral 4 

longitudinal, inferior 3 

superior 3 

occipital 4 

petrosal, inferior 4 

superior 4 

straight 4 

torcular Herophili 3,4 

transverse or basilar 4 

Sixth nerve, origin.. 39. 79, 91, 93, 94 

ventricle 97 

Solly, bundle of 87 

Sommering, nomenclature 92 

Space, anterior perforated 15, 55 

posterior 13, 29, 37, 38 

Spinal accessory nerve, origin .79, 83, 

93, 94 

Spinal bulb 78 

Spinal cord 96-107 

central canal of 97 

columns of 98 

commissures 97-102 

development 96, 52 

enlargements 96, 97 

fissures 97,98 

gray matter 99-102 

ligament, central 6,96 

denticulate 6,97 

roots of nerves 105-107 

tracts of fibers 102-105 

Spinal ganglion 106 

Spongioblasts 52 

Stilling, nuclei of 70, 71, 101 

Striate body 17, 22-24 

Stratum cinereum 43 

dorsale 42 

opticum 43 

zonale 32, 43 

Substantia gelatinosa Rolandi..97, 99 

ferruginea 91 

nigra 33, 37, 38, 58 

spongiosa 99 

Subthalmic region 33 

Subarachnoid fluid 5 

spaces 5 

tissue 5 

Sulci of cerebrum 9-14, 54 

frontal 9 



intraparietal 9 

occipital 10 

olfactory 14 

parallel 10 

postcentral 9 

precentral 9 

primary '. 54 

ofReil 10 

temporal . . 10 

Sulcus basilaris 73, 75 

centralis insulae 10 

lateralis 37 

limitans insulae 10, 14 

mesialis 36 

oculomotorius 37 

valleculas, 66 

Surface of cerebellum 64-69 

of cerebrum 8-16 

of medulla 79-82 

of mid-brain 36, 37 

of pons 73, 74 

of spinal cord 97, 98 

Surcingle 24, 26 

Sustentacular tissue 44 

Sylvius, aqueduct of .. .27, 28, 29, 39, 

49,53,58 

fissure 8, 12,14,48,54 



Taenia semicircularis 22, 24, 26 

tecta 19 

Tapetum 19, 22 

T-branches, cerebellar 70 

spinal nerves (posterior 

roots) 107 

Tegmentum 29, 33, 37, 39-41, 50, 

58 

Tela choroidea, anterior 5, 30, 31 

posterior 5, 81 

Temporal lobe 10 

Tent of fourth ventricle. . ..63, 71, 90 
Tenth nerve, origin, 79, 83, 92, 93, 94 

Tentorium cerebelli 3,8 

Thalamencephalon 53, 57 

Thalamus opticus 20-22, 24, 29, 32- 

6 „ 35,57 

Third nerve, origin. . . . 13, 39, 93, 94 

ventricle 20, 27, 28, 53, 57 

Tonsils of cerebellum 67, 68 



Index. 



117 



Tracts, direct sensory 38 

of spinal cord 102-105 

antero-lateral ground bun- 
dle 80,86, 103 

cerebellar, antero-lateral as- 
cending 80, 86, 104 

antero-lateral descend- 
ing 80, 86, 103 

direct 80, 81, 86, 87, 

104 

comma 105 

marginal (Lissauer's).. 104 

postero-median 105 

postero-lateral 105 

pyramidal 38 

crossed 79, 80, 104 

direct 80, 103 

Tracts, olfactory 15, 92 

optic 14, 57,92 

Transverse fissure, great 8,26 

Trapezium of pons 75 

Trifacial nerve, origin 49, 74, 88, 91, 

93,94 

Trigonum acaustici 91,92 

habenulae 32 

hypoglossi 91,92 

olfactorium 15, 16, 55 

vagi .91, 92 

ventriculi 26 

Tuber annulare 73 

cinereum 12, 29, 49, 57 

valvulae ....67, 68, 69 

Tubercle, cuneate 89 

of Rolando 87 

Tiirck's tracts 103 

Twelfth nerve, origin, 79, 83, 91, 92, 

93,94 

Types of cells (see cells) 44 

Golgi's 45 

u 

Uncinate convolution 11 

funiculus 51 

Uncus hippocampi 11 

Uvula of cerebellum 67, 68 



Vagus (tenth nerve, origin) 79, 83, 

93, 94 

Vallecula of cerebellum 62 

Sylvii 14, 16, 54 

Valve of Vieussens.41, 42, 62, 63, 71, 

74 

Veins, choroid 25 

cerebellar 72 

cerebral ...60, 61 

meningo-rachidian 97 

medulli-spinal 97, 98 

of Galen 3, 25, 60 

of striate body 25, 60 

Velum interpositum.. .5, 8, 30, 56, 57 
medullary, interior . . 62, 63, 71 

superior 42, 62, 63, 71 

Ventricles 52 

fifth 21, 56 

fourth.... 53, 62, 79, 90-92 
lateral... 20, 21, 22-27, 53 

of corpus callosum 19 

of hemispheres 22 

of spinal cord 97 

third 20, 27-35,53, 57 

Vesicles, hemisphere 54 

optic 57 

primary of brain. 52, 53 

secondary of brain 52-58 

Vieussens, valve of (see above) 

Villi of arachnoid 5 

Visual center 9, 10 

W 
White matter of cerebellum.. ..62, 65, 

71, 72 

of cerebrum . . .44, 49-51 

of medulla 82-88 

of mid-brain. . ....44, 50 

of pons 74, 77 

of spinal cord.. 102-107 

Willis, circle of 58 

Worm of cerebellum 62 

inferior 62 

superior 62 

Z 
Zona incerta 34 



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